HttpClient入门

  HttpClient 是apache 组织下的一个用于处理HTTP请求和响应的开源工具。它不是一个浏览器，也不处理客户端缓存等浏览器的功能。它只是一个类库！它在JDK 的基本类库基础上做了更好的封装！HttpClient 项目依赖于HttpCore（处理核心的HTTP 协议）、commons-codec（处理与编码有关的问题的项目）和commons-logging(处理与日志记录有关问题的项目)。

  如果你希望能够通过HttpClient 向服务器上传文件等与multipart编码类型有关的请求，以及其它复杂的MIME 类型，那么，你需要另外一个依赖包：HttpMime（它是专门处理与MIME 类型有关问题的项目），在下载的HttpClient 包中（下载地址为：http://hc.apache.org/downloads.cgi）已经包含了HttpMime。

1. HttpClient的范围

基于HttpCore[http://hc.apache.org/httpcomponents-core/index.html]的客户端HTTP运输实现库

基于经典（阻塞）I/O

内容无关

2. 什么是HttpClient不能做的

HttpClient 不是一个浏览器。它是一个客户端的HTTP通信实现库。HttpClient的目标是发送和接收HTTP报文。HttpClient不会去缓存内容，执行嵌入在HTML页面中的javascript代码，猜测内容类型，重新格式化请求/重定向URI，或者其它和HTTP运输无关的功能。

例子：

import java.util.ArrayList;import java.util.List;import org.apache.http.HttpEntity;import org.apache.http.HttpResponse;import org.apache.http.NameValuePair;import org.apache.http.client.entity.UrlEncodedFormEntity;import org.apache.http.client.methods.HttpGet;import org.apache.http.client.methods.HttpPost;import org.apache.http.impl.client.DefaultHttpClient;import org.apache.http.message.BasicNameValuePair;import org.apache.http.util.EntityUtils;public class QuickStart {    public static void main(String[] args) throws Exception {        DefaultHttpClient httpclient = new DefaultHttpClient();        HttpGet httpGet = new HttpGet("http://targethost/homepage");        HttpResponse response1 = httpclient.execute(httpGet);        // The underlying HTTP connection is still held by the response object         // to allow the response content to be streamed directly from the network socket.         // In order to ensure correct deallocation of system resources         // the user MUST either fully consume the response content  or abort request         // execution by calling HttpGet#releaseConnection().        try {            System.out.println(response1.getStatusLine());            HttpEntity entity1 = response1.getEntity();            // do something useful with the response body            // and ensure it is fully consumed            EntityUtils.consume(entity1);        } finally {            httpGet.releaseConnection();        }        HttpPost httpPost = new HttpPost("http://targethost/login");        List <NameValuePair> nvps = new ArrayList <NameValuePair>();        nvps.add(new BasicNameValuePair("username", "vip"));        nvps.add(new BasicNameValuePair("password", "secret"));        httpPost.setEntity(new UrlEncodedFormEntity(nvps));        HttpResponse response2 = httpclient.execute(httpPost);        try {            System.out.println(response2.getStatusLine());            HttpEntity entity2 = response2.getEntity();            // do something useful with the response body            // and ensure it is fully consumed            EntityUtils.consume(entity2);        } finally {            httpPost.releaseConnection();        }    }}