httpclient4.5 入门教程 1.1执行请求

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转载最新推荐文章于 2026-03-31 04:19:19 发布 504 阅读 AI 写同款· GEO 优化 ›

Httpclient4.5详解之源码解析和使用一: 关键执行流程源码解读前言作为一个java后端开发，调用http协议的请求一直使用的httpclient，但是对他内部原理却一概不知，由于它使用了连接池来解决连接资源消耗所带来的问题，同时我们在使用时他也隐匿了连接池操作的很多细节，所以若是使用不当势必会带来很多隐藏的坑（诸如CLOSE_WAIT过多造成服务假死之类）所以最近有时间看了他内部源码，特此记录下来。 httpclient当前版本总览： httpc... 阅读详情

本文转载自http://blog.youkuaiyun.com/u011179993/article/details/47131773

第一章：基础

1.1执行请求

HttpClient最基本的功能是执行HTTP方法，一个 HTTP 方法的执行包含一个或多个 HTTP 请求/HTTP 相应的交换，通常由 HttpClient的内部来处理。使用者被要求提供一个Request对象来执行，HttpClient就会把请求传送给目标服务器并返回一个相对应的response对象，如果执行不成功，将会抛出一个异常。

显然，HttpClient API 的主要切入点就是定义描述上述契约的HttpClient接口。

一个简单的请求执行事例：

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print ?

CloseableHttpClient httpclient = HttpClients.createDefault();
HttpGet httpget = new HttpGet(“http://localhost/”);
CloseableHttpResponse response = httpclient.execute(httpget);
try {
<…>
} finally {
response.close();
}

CloseableHttpClient httpclient = HttpClients.createDefault();
HttpGet httpget = new HttpGet("http://localhost/");
CloseableHttpResponse response = httpclient.execute(httpget);
try {
   <...>
} finally {
   response.close();
}

1.1.1. HTTP 请求（Request）

所有 HTTP 请求都有一个请求起始行，这个起始行由方法名，请求 URI 和 HTTP 协议版本组成。HttpClient很好地支持了HTTP/1.1规范中所有的HTTP方法：GET，HEAD， POST，PUT， DELETE， TRACE 和 OPTIONS。每个方法都有一个特别的类：HttpGet，HttpHead， HttpPost，HttpPut，HttpDelete，HttpTrace和HttpOptions。URI是统一资源标识符的缩写，用来标识与请求相符合的资源。HTTP 请求URI包含了一个协议名称，主机名，可选端口，资源路径，可选的参数，可选的片段。

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HttpGet httpget = new HttpGet(
”http://www.google.com/search?hl=en&q=httpclient&btnG=Google+Search&aq=f&oq=”);

HttpGet httpget = new HttpGet(
     "http://www.google.com/search?hl=en&q=httpclient&btnG=Google+Search&aq=f&oq=");

HttpClient提供了URIBuilder工具类来简化创建、修改请求 URIs。

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URI uri = new URIBuilder()
.setScheme(”http”)
.setHost(”www.google.com”)
.setPath(”/search”)
.setParameter(”q”, “httpclient”)
.setParameter(”btnG”, “Google Search”)
.setParameter(”aq”, “f”)
.setParameter(”oq”, “”)
.build();
HttpGet httpget = new HttpGet(uri);
System.out.println(httpget.getURI());</span>

URI uri = new URIBuilder()
          .setScheme("http")
          .setHost("www.google.com")
          .setPath("/search")
          .setParameter("q", "httpclient")
          .setParameter("btnG", "Google Search")
          .setParameter("aq", "f")
          .setParameter("oq", "")
          .build();
HttpGet httpget = new HttpGet(uri);
System.out.println(httpget.getURI());</span>

输出：

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http://www.google.com/search?q=httpclient&btnG=Google+Search&aq=f&oq=

http://www.google.com/search?q=httpclient&btnG=Google+Search&aq=f&oq=

1.1.2.HTTP 响应（Response）

HTTP 相应是服务器接收并解析请求信息后返回给客户端的信息，它的起始行包含了一个协议版本，一个状态码和描述状态的短语。

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HttpResponse response = new BasicHttpResponse(HttpVersion.HTTP_1_1
,HttpStatus.SC_OK, ”OK”);
System.out.println(response.getProtocolVersion());
System.out.println(response.getStatusLine().getStatusCode());
System.out.println(response.getStatusLine().getReasonPhrase());
System.out.println(response.getStatusLine().toString());

HttpResponse response = new BasicHttpResponse(HttpVersion.HTTP_1_1
                             ,HttpStatus.SC_OK, "OK");
System.out.println(response.getProtocolVersion());
System.out.println(response.getStatusLine().getStatusCode());
System.out.println(response.getStatusLine().getReasonPhrase());
System.out.println(response.getStatusLine().toString());

输出：

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HTTP/1.1
200
OK
HTTP/1.1 200 OK

HTTP/1.1
200
OK
HTTP/1.1 200 OK

1.1.3.处理报文首部（Headers）

一个HTTP报文包含了许多描述报文的首部，比如内容长度，内容类型等。HttpClient提供了一些方法来取出，添加，移除，枚举首部。

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HttpResponse response = new BasicHttpResponse(HttpVersion.HTTP_1_1,HttpStatus.SC_OK, “OK”);
response.addHeader(”Set-Cookie”,“c1=a; path=/; domain=localhost”);
response.addHeader(”Set-Cookie”,“c2=b; path=\”/\”, c3=c; domain=\”localhost\”“);
Header h1 = response.getFirstHeader(”Set-Cookie”);
System.out.println(h1);
Header h2 = response.getLastHeader(”Set-Cookie”);
System.out.println(h2);
Header[] hs = response.getHeaders(”Set-Cookie”);
System.out.println(hs.length);

HttpResponse response = new BasicHttpResponse(HttpVersion.HTTP_1_1,HttpStatus.SC_OK, "OK");
response.addHeader("Set-Cookie","c1=a; path=/; domain=localhost");
response.addHeader("Set-Cookie","c2=b; path=\"/\", c3=c; domain=\"localhost\"");
Header h1 = response.getFirstHeader("Set-Cookie");
System.out.println(h1);
Header h2 = response.getLastHeader("Set-Cookie");
System.out.println(h2);
Header[] hs = response.getHeaders("Set-Cookie");
System.out.println(hs.length);

输出：
Set-Cookie: c1=a; path=/; domain=localhost
Set-Cookie: c2=b; path=”/”, c3=c; domain=”localhost”
2

获得所有指定类型首部最有效的方式是使用HeaderIterator接口

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HttpResponse response = new BasicHttpResponse(HttpVersion.HTTP_1_1,HttpStatus.SC_OK, “OK”);
response.addHeader(”Set-Cookie”,“c1=a; path=/; domain=localhost”);
response.addHeader(”Set-Cookie”,“c2=b; path=\”/\”, c3=c; domain=\”localhost\”“);
HeaderIterator it = response.headerIterator(”Set-Cookie”);
while (it.hasNext()) {
System.out.println(it.next());
}

HttpResponse response = new BasicHttpResponse(HttpVersion.HTTP_1_1,HttpStatus.SC_OK, "OK");
response.addHeader("Set-Cookie","c1=a; path=/; domain=localhost");
response.addHeader("Set-Cookie","c2=b; path=\"/\", c3=c; domain=\"localhost\"");
HeaderIterator it = response.headerIterator("Set-Cookie");
while (it.hasNext()) {
     System.out.println(it.next());
}

输出：

Set-Cookie: c1=a; path=/; domain=localhost

Set-Cookie: c2=b; path=”/”, c3=c; domain=”localhost”

HttpClient也提供了其他便利的方法吧HTTP报文转化为单个的HTTP元素。

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HttpResponse response = new BasicHttpResponse(HttpVersion.HTTP_1_1,HttpStatus.SC_OK, “OK”);
response.addHeader(”Set-Cookie”,“c1=a; path=/; domain=localhost”);
response.addHeader(”Set-Cookie”,“c2=b; path=\”/\”, c3=c; domain=\”localhost\”“);
HeaderElementIterator it = new BasicHeaderElementIterator(
response.headerIterator(”Set-Cookie”));
while (it.hasNext()) {
HeaderElement elem = it.nextElement();
System.out.println(elem.getName() + ” = ” + elem.getValue());
NameValuePair[] params = elem.getParameters();
for (int i = 0; i < params.length; i++) {
System.out.println(” ” + params[i]);
}
}

HttpResponse response = new BasicHttpResponse(HttpVersion.HTTP_1_1,HttpStatus.SC_OK, "OK");
response.addHeader("Set-Cookie","c1=a; path=/; domain=localhost");
response.addHeader("Set-Cookie","c2=b; path=\"/\", c3=c; domain=\"localhost\"");
HeaderElementIterator it = new BasicHeaderElementIterator(
response.headerIterator("Set-Cookie"));
while (it.hasNext()) {
     HeaderElement elem = it.nextElement();
     System.out.println(elem.getName() + " = " + elem.getValue());
     NameValuePair[] params = elem.getParameters();
     for (int i = 0; i < params.length; i++) {
          System.out.println(" " + params[i]);
     }
}

输出：
c1 = a
path=/
domain=localhost
c2 = b
path=/
c3 = c
domain=localhost

======================================总结区域（非原文）============================

1.对于HttpClient你可以把它简单理解成浏览器就好了。

2.HttpClient请求是必不可少的，所以构建请求很重要，要对HTTP报文有一定的了解。

3.响应不是必须的，因为HttpClient是客户端编程，只是为了方便测试使用。

4.学会处理首部很重要，会面有更加详细的内容。

5.对HTTP协议不是很了解的同学，推荐看《HTTP权威指南》这本书。

其他内容请查看目录贴点击打开链接