HttpClient ---------- 服务器请求外部service

HttpClient是Apache Jakarta Common下的子项目，可以用来提供高校的、最新的、功能丰富的支持HTTP协议的客户端编程工具包，并支持HTTP协议最新的版本和建议。
基于httpClient4.5总结，不同版本有一些变化

功能

1. 实现了所有HTTP的方法（GET, POST, PUT, HEAD等）
2. 支持自动转向
3. 支持HTTPS协议
4. 支持代理服务器等

实现步骤

1. 创建HttpClient实例
   “`java
   HttpClient client = HttpClients.createDefault();

2. 创建某种连接方法的实例Method(GET,POST等)
```java
HttpPost post = new HttpPost(url);
HttpGet get = new HttpGet(url);




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1. 参数设置
   两种方式设置参数的方法：

   • Request-line
     在请求行上通过URI直接提供参数

   直接拼接在URI后面
   pl url? paramA=a¶mB=b
   URIUtils工具类
   pl.
   “`java
   URI uri = URIUtils.createURI(scheme, host, port, path, query, fragment);
   URI uri = URIUtils.createURI(“http”, “localhost”, 80, “/login.html”, “paramA=A¶mB=B”, null);
   URLEncoder.encode(“中国”, “UTF-8”) 解决中文乱码问题

    URLEncodedUtils工具类
    pl.
    ```java
List <NameValuePair> list = new ArrayList<NameValuePair>();
list.add(new BasicNameValuePair("params", "A"));
list.add(new BasicNameValuePair("paramB", "B"));
String param = URLEncodedUtils.format(list, "UTF-8");
//调用URIUtils方法




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• request-body
  将参数放到request-body中。仅用于POST请求
  (1) UrlEncodedFormEntity类
  pl.
  “`java
  List list = new ArrayList();
  list.add(new BasicNameValuePair(“params”, “A”));
  list.add(new BasicNameValuePair(“paramB”, “B”));
  HttpEntity entity = new UrlEncodedFormEntity(list);
  HttpPost post = new HttpPost(url);
  post.setEntity(entity);

    (2) MultipartEntity类
    pl.
    ```java
HttpPost post = new HttpPost(url);
MultipartEntity entity = new MultipartEntity();
ntity.addPart("ParamA", new StringBody("中国", Charset.forName("UTF-8")));
entity.addPart("paramb", new FileBody(new File("c.txt")));
post.setEntity(entity);




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详解： http://http://blog.youkuaiyun.com/chenyi_home/article/details/17240457
(3) MultipartEntityBuilder
pl.

MultipartEntityBuilder  builder = MultipartEntityBuilder.create();
builder.addBinaryBody(name, stream, ContentType.MULTIPART_FORM_DATA, filename);
builder.addTextBody(name, text);
builder.addPart(name, contentBody);
HttpEntity entity = (HttpEntity) builder.create();




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1. HttpClient来执行Method
   pl.

HttpResponse res =  client.execute(post);




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状态判断：

StatusLine statusLine =  res.getStatusLine();
int statusCode = statusLine.getStatusCode();
statusCode == HttpStatus.SC_OK




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HttpStatus 拥有请求的不同的状态:
404 HttpStatus.SC_NOT_ACCEPTABLE
500 HttpStatus.SC_INTERNAL_SERVER_ERROR
200 HttpStatus.SC_OK
请求转发的状态码：
301 HttpStatus.SC_MOVED_TEMPORARILY
302 HttpStatus.SC_MOVED_PERMANENTLY
303 HttpStatus.SC_SEE_OTHER
307 HttpStatus.SC_TEMPORARY_REDIRECT
转发代码（自动转向）：

if (statusCode == HttpStatus.SC_SEE_OTHER) {
    Header[] Headers = res.getHeaders("location");
    for (Header header: Headers) {
        String newUrl = header.getValue();
        //重新请求
    }
}




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Http协议状态码：http://www.cnblogs.com/shanyou/archive/2012/05/06/2486134.html

1. 读取response
   pl.

HttpEntity entity =  res.getEntity();
InputStream in = entity.getContent();
String content = entity.toString();

6 释放链接，处理业务
最新几个版本不需要自己释放链接
得到in, content处理业务

HttpEntity

BasicHttpEntity  底层流的基本实体， 通常为在http报文中获取的实体
ByteArrayEntity  从指定字节数组中取出内容实体
StringEntity   通过String创建的实体
InputStreamEntity
FileEntity
EntityTemplete    从ContentProducer获取内容的实体
HttpEntityWrapper  实体类的代理类
BufferedHttpEntity HttpEntityWrapper的子类

详情：http://blog.youkuaiyun.com/haluoluo211/article/details/52085880