OkHttp使用完全教程

1. 历史上Http请求库优缺点

在讲述OkHttp之前, 我们看下没有OkHttp的时代, 我们是如何完成http请求的. 
在没有OkHttp的日子, 我们使用HttpURLConnection或者HttpClient. 那么这两者都有什么优缺点呢? 为什么不在继续使用下去呢? 
HttpClient是Apache基金会的一个开源网络库, 功能十分强大, API数量众多, 但是正是由于庞大的API数量使得我们很难在不破坏兼容性的情况下对它进行升级和扩展, 所以Android团队在提升和优化HttpClient方面的工作态度并不积极. 
HttpURLConnection是一种多用途, 轻量极的HTTP客户端, 提供的API比较简单, 可以容易地去使用和扩展. 不过在Android 2.2版本之前,HttpURLConnection一直存在着一些令人厌烦的bug. 比如说对一个可读的InputStream调用close()方法时，就有可能会导致连接池失效了。那么我们通常的解决办法就是直接禁用掉连接池的功能：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">disableConnectionReuseIfNecessary</span>() {    
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 这是一个2.2版本之前的bug    </span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (Integer.parseInt(Build.VERSION.SDK) < Build.VERSION_CODES.FROYO) {    
        System.setProperty(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http.keepAlive"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"false"</span>);    
    }    
}    </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

因此, 一般的推荐是在2.2之前, 使用HttpClient, 因为其bug较少. 在2.2之后, 推荐使用HttpURLConnection, 因为API简单, 体积小, 并且有压缩和缓存机制, 并且Android团队后续会继续优化HttpURLConnection.

但是, 上面两个类库和OkHttp比起来就弱爆了, 因为OkHttp不仅具有高效的请求效率, 并且提供了很多开箱即用的网络疑难杂症解决方案. 
- 支持HTTP/2, HTTP/2通过使用多路复用技术在一个单独的TCP连接上支持并发, 通过在一个连接上一次性发送多个请求来发送或接收数据 
- 如果HTTP/2不可用, 连接池复用技术也可以极大减少延时 
- 支持GZIP, 可以压缩下载体积 
- 响应缓存可以直接避免重复请求 
- 会从很多常用的连接问题中自动恢复 
- 如果您的服务器配置了多个IP地址, 当第一个IP连接失败的时候, OkHttp会自动尝试下一个IP 
- OkHttp还处理了代理服务器问题和SSL握手失败问题

使用 OkHttp 无需重写您程序中的网络代码。OkHttp实现了几乎和Java.net.HttpURLConnection一样的API。如果你用了 Apache HttpClient，则OkHttp也提供了一个对应的okhttp-apache 模块。

还有一个好消息, 从Android 4.4起, 其HttpURLConnection的内部实现已经变为OkHttp, 您可以参考这两个网页:爆栈网和Twitter.

2. OkHttp类与http请求响应的映射

在讲解OkHttp使用之前, 再看下我们Http请求和响应都有哪些部分组成.

2.1 http请求

 
所以一个类库要完成一个http请求, 需要包含 请求方法, 请求地址, 请求协议, 请求头, 请求体这五部分. 这些都在okhttp3.Request的类中有体现, 这个类正是代表http请求的类. 看下图: 
 
其中HttpUrl类代表请求地址, String method代表请求方法, Headers代表请求头, RequestBody代表请求体. Object tag这个是用来取消http请求的标志, 这个我们先不管. 这里也许你在疑惑, 请求协议呢? 为什么没有请求协议对应的类. 且听我慢慢道来, 下面就会讲到这个问题.

2.1.1 请求协议的协商升级

目前, Http/1.1在全世界大范围的使用中, 直接废弃跳到http/2肯定不现实. 不是每个用户的浏览器都支持http/2的, 也不是每个服务器都打算支持http/2的, 如果我们直接发送http/2格式的协议, 服务器又不支持, 那不是挂掉了! 总不能维护一个全世界的网站列表, 表示哪些支持http/2, 哪些不支持? 
为了解决这个问题, 从稍高层次上来说, 就是为了更方便地部署新协议, HTTP/1.1 引入了 Upgrade 机制. 这个机制在 RFC7230 的「6.7 Upgrade」这一节中有详细描述. 
简单说来, 就是先问下你支持http/2么? 如果你支持, 那么接下来我就用http/2和你聊天. 如果你不支持, 那么我还是用原来的http/1.1和你聊天.

1.客户端在请求头部中指定Connection和Upgrade两个字段发起 HTTP/1.1 协议升级. HTTP/2 的协议名称是 h2c, 代表 HTTP/2 ClearText.

<code class="hljs http has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-request" style="color: rgb(0, 0, 136); box-sizing: border-box;">GET <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">/</span> HTTP/1.1</span>
<span class="hljs-attribute" style="box-sizing: border-box;">Host</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">example.com</span>
<span class="hljs-attribute" style="box-sizing: border-box;">Connection</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">Upgrade, HTTP2-Settings</span>
<span class="hljs-attribute" style="box-sizing: border-box;">Upgrade</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">h2c</span>
<span class="hljs-attribute" style="box-sizing: border-box;">HTTP2-Settings</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;"><base64url encoding of HTTP/2 SETTINGS payload></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

2.如果服务端不同意升级或者不支持 Upgrade 所列出的协议，直接忽略即可（当成 HTTP/1.1 请求，以 HTTP/1.1 响应）.

<code class="hljs http has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-status" style="color: rgb(0, 0, 136); box-sizing: border-box;">HTTP/1.1 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">200</span> OK</span>
<span class="hljs-attribute" style="box-sizing: border-box;">Content-Length</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">243</span>
<span class="hljs-attribute" style="box-sizing: border-box;">Content-Type</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">text/html</span>

<span class="r" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

如果服务端同意升级，那么需要这样响应：

<code class="hljs http has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-status" style="color: rgb(0, 0, 136); box-sizing: border-box;">HTTP/1.1 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span> Switching Protocols</span>
<span class="hljs-attribute" style="box-sizing: border-box;">Connection</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">Upgrade</span>
<span class="hljs-attribute" style="box-sizing: border-box;">Upgrade</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">h2c</span>

<span class="r" style="box-sizing: border-box;">[ HTTP/<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> connection <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span> ]</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

HTTP Upgrade 响应的状态码是 101，并且响应正文可以使用新协议定义的数据格式。

这样就可以完成从http/1.1升级到http/2了. 同样也可以从http/1.1升级到WebSocket.

这样, 你就了解了为什么OkHttp没有指定具体请求协议了吧. 因为OkHttp使用了请求协议的协商升级, 无论是1.1还是2, 都先只以1.1来发送, 并在发送的信息头里包含协议升级字段. 接下来就看服务器是否支持协议升级了. OkHttp使用的协议升级字段是ALPN, 如果有兴趣, 可以更深入的查阅相关资料.

2.1.2 OkHttp请求

接下来我们构造一个http请求, 并查看请求具体内容.

<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">final <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span>.Builder().url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"https://github.com/"</span>).build();</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

我们看下在内存中, 这个请求是什么样子的, 是否如我们上文所说和请求方法, 请求地址, 请求头, 请求体一一对应. 

2.2 http响应

我们看下一个http响应由哪些部分组成, 先看下响应组成图: 
 
可以看到大体由应答首行, 应答头, 应答体构成. 但是应答首行表达的信息过多, HTTP/1.1表示访问协议, 200是响应码, OK是描述状态的消息. 根据单一职责, 我们不应该把这么多内容用一个应答首行来表示. 这样的话, 我们的响应就应该由访问协议, 响应码, 描述信息, 响应头, 响应体来组成.

2.2.1 OkHttp响应

我们看下OkHttp库怎么表示一个响应: 
 
可以看到Response类里面有Protocol代表请求协议, int code代表响应码, String message代表描述信息, Headers代表响应头, ResponseBody代表响应体. 当然除此之外, 还有Request代表持有的请求, Handshake代表SSL/TLS握手协议验证时的信息, 这些额外信息我们暂时不问.

有了刚才说的OkHttp响应的类组成, 我们看下OkHttp请求后响应在内存中的内容:

<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">final <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span>.Builder().url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"https://github.com/"</span>).build();
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Response</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span> = client.newCall(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>).<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">execute</span>();</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>

 
可以看到和我们的分析十分一致.

讲了OkHttp里的请求类和响应类, 我们接下来就可以直接讲述OkHttp的使用方法了.

3 HTTP GET

3.1 同步GET

同步GET的意思是一直等待http请求, 直到返回了响应. 在这之间会阻塞进程, 所以通过get不能在Android的主线程中执行, 否则会报错.

<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final OkHttpClient client = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> void run() throws Exception {
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span>.Builder()
        .url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://publicobject.com/helloworld.txt"</span>)
        .build();

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Response</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span> = client.newCall(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>).<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">execute</span>();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.isSuccessful()) throw <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>);

    Headers responseHeaders = <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.headers();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < responseHeaders.size(); i++) {
      System.out.println(responseHeaders.name(i) + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">": "</span> + responseHeaders.value(i));
    }

    System.out.println(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.body().<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">string</span>());
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>

OkHttpClient实现了Call.Factory接口, 是Call的工厂类, Call负责发送执行请求和读取响应. 
Request代表Http请求, 通过Request.Builder辅助类来构建. 
client.newCall(request)通过传入一个http request, 返回一个Call调用. 然后执行execute()方法, 同步获得 
Response代表Http请求的响应. response.body()是ResponseBody类, 代表响应体, 可以通过responseBody.string()获得字符串的表达形式, 或responseBody.bytes()获得字节数组的表达形式, 这两种形式都会把文档加入到内存. 也可以通过responseBody.charStream()和responseBody.byteStream()返回流来处理.

上述代码完成的功能是下载一个文件, 打印他的响应头, 以string形式打印响应体. 
响应体的string()方法对于小文档来说十分方便高效. 但是如果响应体太大（超过1MB）, 应避免使用 string()方法, 因为它会将把整个文档加载到内存中. 
对于超过1MB的响应body, 应使用流的方式来处理响应body. 这和我们处理xml文档的逻辑是一致的, 小文件可以载入内存树状解析, 大文件就必须流式解析.

3.2 异步GET

异步GET是指在另外的工作线程中执行http请求, 请求时不会阻塞当前的线程, 所以可以在Android主线程中使用. 
下面是在一个工作线程中下载文件, 当响应可读时回调Callback接口. 当响应头准备好后, 就会调用Callback接口, 所以读取响应体时可能会阻塞. OkHttp现阶段不提供异步api来接收响应体。

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> OkHttpClient client = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> Exception {
    Request request = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Request.Builder()
        .url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://publicobject.com/helloworld.txt"</span>)
        .build();

    client.newCall(request).enqueue(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Callback() {
      <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onFailure</span>(Request request, Throwable throwable) {
        throwable.printStackTrace();
      }

      <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">onResponse</span>(Response response) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!response.isSuccessful()) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + response);

        Headers responseHeaders = response.headers();
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < responseHeaders.size(); i++) {
          System.out.println(responseHeaders.name(i) + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">": "</span> + responseHeaders.value(i));
        }

        System.out.println(response.body().string());
      }
    });
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul>

4 HTTP POST

4.1 Post方式提交String

下面是使用HTTP POST提交请求到服务. 这个例子提交了一个markdown文档到web服务, 以HTML方式渲染markdown. 因为整个请求体都在内存中, 因此避免使用此api提交大文档（大于1MB）.

<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> static final MediaType MEDIA_TYPE_MARKDOWN
  = MediaType.parse(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"text/x-markdown; charset=utf-8"</span>);

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final OkHttpClient client = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> void run() throws Exception {
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span> postBody = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">""</span>
        + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Releases\n"</span>
        + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"--------\n"</span>
        + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"\n"</span>
        + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" * _1.0_ May 6, 2013\n"</span>
        + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" * _1.1_ June 15, 2013\n"</span>
        + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" * _1.2_ August 11, 2013\n"</span>;

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span>.Builder()
        .url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"https://api.github.com/markdown/raw"</span>)
        .post(RequestBody.create(MEDIA_TYPE_MARKDOWN, postBody))
        .build();

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Response</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span> = client.newCall(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>).<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">execute</span>();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.isSuccessful()) throw <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>);

    System.out.println(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.body().<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">string</span>());
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul>

4.2 Post方式提交流

以流的方式POST提交请求体. 请求体的内容由流写入产生. 这个例子是流直接写入Okio的BufferedSink. 你的程序可能会使用OutputStream, 你可以使用BufferedSink.outputStream()来获取. OkHttp的底层对流和字节的操作都是基于Okio库, Okio库也是Square开发的另一个IO库, 填补I/O和NIO的空缺, 目的是提供简单便于使用的接口来操作IO.

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> MediaType MEDIA_TYPE_MARKDOWN
      = MediaType.parse(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"text/x-markdown; charset=utf-8"</span>);

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> OkHttpClient client = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> Exception {
    RequestBody requestBody = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> RequestBody() {
      <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> MediaType <span class="hljs-title" style="box-sizing: border-box;">contentType</span>() {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> MEDIA_TYPE_MARKDOWN;
      }

      <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">writeTo</span>(BufferedSink sink) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> IOException {
        sink.writeUtf8(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Numbers\n"</span>);
        sink.writeUtf8(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"-------\n"</span>);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>; i <= <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">997</span>; i++) {
          sink.writeUtf8(String.format(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" * %s = %s\n"</span>, i, factor(i)));
        }
      }

      <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> String <span class="hljs-title" style="box-sizing: border-box;">factor</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> n) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>; i < n; i++) {
          <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> x = n / i;
          <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (x * i == n) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> factor(x) + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" × "</span> + i;
        }
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> Integer.toString(n);
      }
    };

    Request request = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Request.Builder()
        .url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"https://api.github.com/markdown/raw"</span>)
        .post(requestBody)
        .build();

    Response response = client.newCall(request).execute();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!response.isSuccessful()) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + response);

    System.out.println(response.body().string());
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li></ul>

4.3 Post方式提交文件

以文件作为请求体是十分简单的。

<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> static final MediaType MEDIA_TYPE_MARKDOWN
  = MediaType.parse(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"text/x-markdown; charset=utf-8"</span>);

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final OkHttpClient client = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient();

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> void run() throws Exception {
    File file = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> File(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"README.md"</span>);

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span>.Builder()
        .url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"https://api.github.com/markdown/raw"</span>)
        .post(RequestBody.create(MEDIA_TYPE_MARKDOWN, file))
        .build();

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Response</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span> = client.newCall(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>).<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">execute</span>();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.isSuccessful()) throw <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>);

    System.out.println(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.body().<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">string</span>());
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>

4.4 Post方式提交表单

使用FormEncodingBuilder来构建和HTML<form>标签相同效果的请求体. 键值对将使用一种HTML兼容形式的URL编码来进行编码.

<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final OkHttpClient client = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient();

  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> void run() throws Exception {
    RequestBody formBody = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> FormBody.Builder()
        .add(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"search"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Jurassic Park"</span>)
        .build();
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span>.Builder()
        .url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"https://en.wikipedia.org/w/index.php"</span>)
        .post(formBody)
        .build();

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Response</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span> = client.newCall(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>).<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">execute</span>();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.isSuccessful()) throw <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>);

    System.out.println(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.body().<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">string</span>());
  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>

4.5 Post方式提交分块请求

MultipartBody.Builder可以构建复杂的请求体, 与HTML文件上传形式兼容. 多块请求体中每块请求都是一个请求体, 可以定义自己的请求头. 这些请求头可以用来描述这块请求, 例如它的Content-Disposition. 如果Content-Length和Content-Type可用的话, 他们会被自动添加到请求头中.

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> String IMGUR_CLIENT_ID = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"..."</span>;
  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> MediaType MEDIA_TYPE_PNG = MediaType.parse(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"image/png"</span>);

  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> OkHttpClient client = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient();

  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> Exception {
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Use the imgur image upload API as documented at https://api.imgur.com/endpoints/image</span>
    RequestBody requestBody = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"title"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Square Logo"</span>)
        .addFormDataPart(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"image"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"logo-square.png"</span>,
            RequestBody.create(MEDIA_TYPE_PNG, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> File(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"website/static/logo-square.png"</span>)))
        .build();

    Request request = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Request.Builder()
        .header(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Authorization"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Client-ID "</span> + IMGUR_CLIENT_ID)
        .url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"https://api.imgur.com/3/image"</span>)
        .post(requestBody)
        .build();

    Response response = client.newCall(request).execute();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!response.isSuccessful()) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throw</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + response);

    System.out.println(response.body().string());
  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li></ul>

5. 其他用法

5.1 提取响应头

典型的HTTP头像是一个Map<String, String> : 每个字段都有一个或没有值. 但是一些头允许多个值, 像Guava的Multimap. 
例如: HTTP响应里面提供的Vary响应头, 就是多值的. OkHttp的api试图让这些情况都适用. 
当写请求头的时候, 使用header(name, value)可以设置唯一的name、value. 如果已经有值, 旧的将被移除, 然后添加新的. 使用addHeader(name, value)可以添加多值（添加, 不移除已有的）. 
当读取响应头时, 使用header(name)返回最后出现的name、value. 通常情况这也是唯一的name、value. 如果没有值, 那么header(name)将返回null. 如果想读取字段对应的所有值, 使用headers(name)会返回一个list. 
为了获取所有的Header, Headers类支持按index访问.

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">private final OkHttpClient client = new OkHttpClient()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

public void run() throws Exception {
    Request request = new Request<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Builder</span>()
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.url</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"https://api.github.com/repos/square/okhttp/issues"</span>)
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.header</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"User-Agent"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"OkHttp Headers.java"</span>)
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addHeader</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Accept"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"application/json; q=0.5"</span>)
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addHeader</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Accept"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"application/vnd.github.v3+json"</span>)
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    Response response = client<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newCall</span>(request)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.execute</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    if (!response<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isSuccessful</span>()) throw new IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + response)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Server: "</span> + response<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.header</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Server"</span>))<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Date: "</span> + response<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.header</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Date"</span>))<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Vary: "</span> + response<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.headers</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Vary"</span>))<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>

5.2 使用Gson来解析JSON响应

Gson是一个在JSON和Java对象之间转换非常方便的api库. 这里我们用Gson来解析Github API的JSON响应. 
注意: ResponseBody.charStream()使用响应头Content-Type指定的字符集来解析响应体. 默认是UTF-8.

<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final OkHttpClient client = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient();
  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final Gson gson = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Gson();

  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> void run() throws Exception {
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span>.Builder()
        .url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"https://api.github.com/gists/c2a7c39532239ff261be"</span>)
        .build();
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Response</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span> = client.newCall(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>).<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">execute</span>();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.isSuccessful()) throw <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>);

    Gist gist = gson.fromJson(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.body().charStream(), Gist.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span>);
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (Map.Entry<<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span>, GistFile> entry : gist.files.entrySet()) {
      System.out.println(entry.getKey());
      System.out.println(entry.getValue().content);
    }
  }

  static <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> Gist {
    Map<<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span>, GistFile> files;
  }

  static <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> GistFile {
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span> content;
  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul>

5.3 响应缓存

为了缓存响应, 你需要一个你可以读写的缓存目录, 和缓存大小的限制. 这个缓存目录应该是私有的, 不信任的程序应不能读取缓存内容. 
一个缓存目录同时拥有多个缓存访问是错误的. 大多数程序只需要调用一次new OkHttp(), 在第一次调用时配置好缓存, 然后其他地方只需要调用这个实例就可以了. 否则两个缓存示例互相干扰, 破坏响应缓存, 而且有可能会导致程序崩溃. 
响应缓存使用HTTP头作为配置. 你可以在请求头中添加Cache-Control: max-stale=3600 , OkHttp缓存会支持. 你的服务通过响应头确定响应缓存多长时间, 例如使用Cache-Control: max-age=9600.

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">private final OkHttpClient client<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

public CacheResponse(File cacheDirectory) throws Exception {
    int cacheSize = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1024</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1024</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">; // 10 MiB</span>
    Cache cache = new Cache(cacheDirectory, cacheSize)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    client = new OkHttpClient()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    client<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setCache</span>(cache)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
}

public void run() throws Exception {
    Request request = new Request<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Builder</span>()
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.url</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://publicobject.com/helloworld.txt"</span>)
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    Response response1 = client<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newCall</span>(request)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.execute</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    if (!response1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isSuccessful</span>()) throw new IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + response1)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    String response1Body = response1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.body</span>()<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.string</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 1 response:          "</span> + response1)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 1 cache response:    "</span> + response1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.cacheResponse</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 1 network response:  "</span> + response1<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.networkResponse</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    Response response2 = client<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newCall</span>(request)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.execute</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    if (!response2<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isSuccessful</span>()) throw new IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + response2)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    String response2Body = response2<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.body</span>()<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.string</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 2 response:          "</span> + response2)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 2 cache response:    "</span> + response2<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.cacheResponse</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 2 network response:  "</span> + response2<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.networkResponse</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 2 equals Response 1? "</span> + response1Body<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.equals</span>(response2Body))<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li></ul>

如果需要阻值response使用缓存, 使用CacheControl.FORCE_NETWORK. 如果需要阻值response使用网络, 使用CacheControl.FORCE_CACHE. 
警告: 如果你使用FORCE_CACHE, 但是response要求使用网络, OkHttp将会返回一个504 Unsatisfiable Request响应.

5.3.1 Force a Network Response

有些时候, 比如用户刚刚点击刷新按钮, 这时必须跳过缓存, 直接从服务器抓取数据. 为了强制全面刷新, 我们需要添加no-cache指令:

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">connection<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addRequestProperty</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Cache-Control"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"no-cache"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

这样就可以强制每次请求直接发送给源服务器, 而不经过本地缓存版本的校验, 常用于需要确认认证的应用和严格要求使用最新数据的应用.

5.3.2 Force a Cache Response

有时你会想立即显示资源. 这样即使在后台正下载着最新资源, 你的客户端仍然可以先显示原有资源, 毕竟有个东西显示比没有东西显示要好. 
如果需要限制让请求优先使用本地缓存资源, 需要增加only-if-cached指令:

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
     connection.addRequestProperty(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Cache-Control"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"only-if-cached"</span>);
     InputStream cached = connection.getInputStream();
     <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// the resource was cached! show it</span>
  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (FileNotFoundException e) {
     <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// the resource was not cached</span>
 }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

5.4 取消一个Call

使用Call.cancel()可以立即停止掉一个正在执行的call. 如果一个线程正在写请求或者读响应, 将会引发IOException. 当call没有必要的时候, 使用这个api可以节约网络资源. 例如当用户离开一个应用时, 不管同步还是异步的call都可以取消. 
你可以通过tags来同时取消多个请求. 当你构建一请求时, 使用RequestBuilder.tag(tag)来分配一个标签, 之后你就可以用OkHttpClient.cancel(tag)来取消所有带有这个tag的call.

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">  private final ScheduledExecutorService executor = Executors<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newScheduledThreadPool</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
  private final OkHttpClient client = new OkHttpClient()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

  public void run() throws Exception {
    Request request = new Request<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Builder</span>()
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.url</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://httpbin.org/delay/2"</span>) // This URL is served with a <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> second delay.
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    final long startNanos = System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.nanoTime</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    final <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Call</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">call</span> = client<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newCall</span>(request)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    // Schedule a job to cancel the <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">call</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> second.
    executor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.schedule</span>(new Runnable() {
      @Override public void run() {
        System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%.2f Canceling call.%n"</span>, (System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.nanoTime</span>() - startNanos) / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1e9</span>f)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">call</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.cancel</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
        System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%.2f Canceled call.%n"</span>, (System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.nanoTime</span>() - startNanos) / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1e9</span>f)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
      }
    }, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, TimeUnit<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.SECONDS</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    try {
      System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%.2f Executing call.%n"</span>, (System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.nanoTime</span>() - startNanos) / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1e9</span>f)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
      Response response = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">call</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.execute</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
      System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%.2f Call was expected to fail, but completed: %s%n"</span>,
          (System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.nanoTime</span>() - startNanos) / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1e9</span>f, response)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    } catch (IOException e) {
      System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%.2f Call failed as expected: %s%n"</span>,
          (System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.nanoTime</span>() - startNanos) / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1e9</span>f, e)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    }
  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li></ul>

5.5 超时

没有响应时使用超时结束call. 没有响应的原因可能是客户点链接问题、服务器可用性问题或者这之间的其他东西. OkHttp支持连接超时, 读取超时和写入超时.

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> OkHttpClient client;

  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">ConfigureTimeouts</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> Exception {
    client = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient.Builder()
        .connectTimeout(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, TimeUnit.SECONDS)
        .writeTimeout(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, TimeUnit.SECONDS)
        .readTimeout(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">30</span>, TimeUnit.SECONDS)
        .build();
  }

  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> Exception {
    Request request = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Request.Builder()
        .url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://httpbin.org/delay/2"</span>) <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// This URL is served with a 2 second delay.</span>
        .build();

    Response response = client.newCall(request).execute();
    System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response completed: "</span> + response);
  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>

5.6 每个call的配置

使用OkHttpClient, 所有的HTTP Client配置包括代理设置、超时设置、缓存设置. 当你需要为单个call改变配置的时候, 调用OkHttpClient.newBuilder(). 这个api将会返回一个builder, 这个builder和原始的client共享相同的连接池, 分发器和配置. 
下面的例子中，我们让一个请求是500ms的超时、另一个是3000ms的超时。

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">  private final OkHttpClient client = new OkHttpClient()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

  public void run() throws Exception {
    Request request = new Request<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Builder</span>()
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.url</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://httpbin.org/delay/1"</span>) // This URL is served with a <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> second delay.
        <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

    try {
      // Copy to customize OkHttp for this request.
      OkHttpClient copy = client<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newBuilder</span>()
          <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.readTimeout</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">500</span>, TimeUnit<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.MILLISECONDS</span>)
          <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

      Response response = copy<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newCall</span>(request)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.execute</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
      System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 1 succeeded: "</span> + response)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    } catch (IOException e) {
      System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 1 failed: "</span> + e)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    }

    try {
      // Copy to customize OkHttp for this request.
      OkHttpClient copy = client<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newBuilder</span>()
          <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.readTimeout</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3000</span>, TimeUnit<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.MILLISECONDS</span>)
          <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>

      Response response = copy<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newCall</span>(request)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.execute</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
      System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 2 succeeded: "</span> + response)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    } catch (IOException e) {
      System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Response 2 failed: "</span> + e)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
    }
  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li></ul>

5.7 处理验证

这部分和HTTP AUTH有关.

5.7.1 HTTP AUTH

使用HTTP AUTH需要在server端配置http auth信息, 其过程如下: 
- 客户端发送http请求 
- 服务器发现配置了http auth, 于是检查request里面有没有”Authorization”的http header 
- 如果有, 则判断Authorization里面的内容是否在用户列表里面, Authorization header的典型数据为”Authorization: Basic jdhaHY0=”, 其中Basic表示基础认证, jdhaHY0=是base64编码的”user:passwd”字符串. 如果没有，或者用户密码不对，则返回http code 401页面给客户端. 
- 标准的http浏览器在收到401页面之后, 应该弹出一个对话框让用户输入帐号密码; 并在用户点确认的时候再次发出请求, 这次请求里面将带上Authorization header.

一次典型的访问场景是：

• 浏览器发送http请求（没有Authorization header）
• 服务器端返回401页面
• 浏览器弹出认证对话框
• 用户输入帐号密码，并点确认
• 浏览器再次发出http请求（带着Authorization header）
• 服务器端认证通过，并返回页面
• 浏览器显示页面

5.7.2 OkHttp认证

OkHttp会自动重试未验证的请求. 当响应是401 Not Authorized时，Authenticator会被要求提供证书. Authenticator的实现中需要建立一个新的包含证书的请求. 如果没有证书可用, 返回null来跳过尝试. 
使用Response.challenges()来获得任何authentication challenges的 schemes 和 realms. 当完成一个Basic challenge, 使用Credentials.basic(username, password)来解码请求头.

<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final OkHttpClient client;

  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Authenticate() {
    client = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> OkHttpClient.Builder()
        .authenticator(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Authenticator() {
          @Override <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span> authenticate(Route route, <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Response</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>) throws IOException {
            System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Authenticating for response: "</span> + <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>);
            System.out.println(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Challenges: "</span> + <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.challenges());
            <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span> credential = Credentials.basic(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"jesse"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"password1"</span>);
            return <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>().newBuilder()
                .header(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Authorization"</span>, credential)
                .build();
          }
        })
        .build();
  }

  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> void run() throws Exception {
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span>.Builder()
        .url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"http://publicobject.com/secrets/hellosecret.txt"</span>)
        .build();

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Response</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span> = client.newCall(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>).<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">execute</span>();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.isSuccessful()) throw <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> IOException(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Unexpected code "</span> + <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>);

    System.out.println(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.body().<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">string</span>());
  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li></ul>

当认证无法工作时, 为了避免多次重试, 你可以返回空来放弃认证. 例如, 当exact credentials已经尝试过, 你可能会直接想跳过认证, 可以这样做:

<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (credential<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">equals</span>(response<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>request()<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">header</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Authorization"</span>))) {
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">null</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// If we already failed with these credentials, don't retry.</span>
   }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

当重试次数超过定义的次数, 你若想跳过认证, 可以这样做:

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (responseCount(response) >= <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>) {
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// If we've failed 3 times, give up.</span>
  }

  <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-title" style="box-sizing: border-box;">responseCount</span>(Response response) {
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> result = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> ((response = response.priorResponse()) != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {
      result++;
    }
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> result;
  }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>

这样, 对OkHttp的使用我们就讲完了, 下一节会讲OkHttp内部实现.

出处：http://blog.youkuaiyun.com/oncealong/article/details/52096477