　　Http协议的重要性相信不用我多说了，HttpClient相比传统JDK自带的URLConnection，增加了易用性和灵活性（具体区别，日后我们再讨论），它不仅是客户端发送Http请求变得容易，而且也方便了开发人员测试接口（基于Http协议的），即提高了开发的效率，也方便提高代码的健壮性。因此熟练掌握HttpClient是很重要的必修内容，掌握HttpClient后，相信对于Http协议的了解会更加深入。

一、简介

HttpClient是Apache Jakarta Common下的子项目，用来提供高效的、最新的、功能丰富的支持HTTP协议的客户端编程工具包，并且它支持HTTP协议最新的版本和建议。 HttpClient已经应用在很多的项目中，比如Apache Jakarta上很著名的另外两个开源项目Cactus和HTMLUnit都使用了HttpClient。

下载地址: http://hc.apache.org/downloads.cgi

二、特性

1. 基于标准、纯净的java语言。实现了Http1.0和Http1.1

2. 以可扩展的面向对象的结构实现了Http全部的方法（GET, POST, PUT, DELETE, HEAD, OPTIONS, and TRACE）。

3. 支持HTTPS协议。

4. 通过Http代理建立透明的连接。

5. 利用CONNECT方法通过Http代理建立隧道的https连接。

6. Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session, SNPNEGO/Kerberos认证方案。

7. 插件式的自定义认证方案。

8. 便携可靠的套接字工厂使它更容易的使用第三方解决方案。

9. 连接管理器支持多线程应用。支持设置最大连接数，同时支持设置每个主机的最大连接数，发现并关闭过期的连接。

10. 自动处理Set-Cookie中的Cookie。

11. 插件式的自定义Cookie策略。

12. Request的输出流可以避免流中内容直接缓冲到socket服务器。

13. Response的输入流可以有效的从socket服务器直接读取相应内容。

14. 在http1.0和http1.1中利用KeepAlive保持持久连接。

15. 直接获取服务器发送的response code和 headers。

16. 设置连接超时的能力。

17. 实验性的支持http1.1 response caching。

18. 源代码基于Apache License 可免费获取。

三、使用方法

使用HttpClient发送请求、接收响应很简单，一般需要如下几步即可。

1. 创建HttpClient对象。

2. 创建请求方法的实例，并指定请求URL。如果需要发送GET请求，创建HttpGet对象；如果需要发送POST请求，创建HttpPost对象。

3. 如果需要发送请求参数，可调用HttpGet、HttpPost共同的
setParams(HetpParams
params)方法来添加请求参数；对于HttpPost对象而言，也可调用setEntity(HttpEntity
entity)方法来设置请求参数。

4. 调用HttpClient对象的execute(HttpUriRequest request)发送请求，该方法返回一个HttpResponse。

5. 调用HttpResponse的getAllHeaders()、
getHeaders(String
name)等方法可获取服务器的响应头；调用HttpResponse的getEntity()方法可获取HttpEntity对象，该对象包装了服务器
的响应内容。程序可通过该对象获取服务器的响应内容。

6. 释放连接。无论执行方法是否成功，都必须释放连接

四、实例

package com.test;

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.UnsupportedEncodingException;

import java.security.KeyManagementException;

import java.security.KeyStore;

import java.security.KeyStoreException;

import java.security.NoSuchAlgorithmException;

import java.security.cert.CertificateException;

import java.util.ArrayList;

import java.util.List;

import javax.net.ssl.SSLContext;

import org.apache.http.HttpEntity;

import org.apache.http.NameValuePair;

import org.apache.http.ParseException;

import org.apache.http.client.ClientProtocolException;

import org.apache.http.client.entity.UrlEncodedFormEntity;

import org.apache.http.client.methods.CloseableHttpResponse;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.client.methods.HttpPost;

import org.apache.http.conn.ssl.SSLConnectionSocketFactory;

import org.apache.http.conn.ssl.SSLContexts;

import org.apache.http.conn.ssl.TrustSelfSignedStrategy;

import org.apache.http.entity.ContentType;

import org.apache.http.entity.mime.MultipartEntityBuilder;

import org.apache.http.entity.mime.content.FileBody;

import org.apache.http.entity.mime.content.StringBody;

import org.apache.http.impl.client.CloseableHttpClient;

import org.apache.http.impl.client.HttpClients;

import org.apache.http.message.BasicNameValuePair;

import org.apache.http.util.EntityUtils;

import org.junit.Test;

public class HttpClientTest {

	@Test

	public void jUnitTest() {

		get();

	}

	/**

	 * HttpClient连接SSL

	 */

	public void ssl() {

		CloseableHttpClient httpclient = null;

		try {

			KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());

			FileInputStream instream = new FileInputStream(new File("d:\\tomcat.keystore"));

			try {

				// 加载keyStore d:\\tomcat.keystore

				trustStore.load(instream, "123456".toCharArray());

			} catch (CertificateException e) {

				e.printStackTrace();

			} finally {

				try {

					instream.close();

				} catch (Exception ignore) {

				}

			}

			// 相信自己的CA和所有自签名的证书

			SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(trustStore, new TrustSelfSignedStrategy()).build();

			// 只允许使用TLSv1协议

			SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslcontext, new String[] { "TLSv1" }, null,

					SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER);

			httpclient = HttpClients.custom().setSSLSocketFactory(sslsf).build();

			// 创建http请求(get方式)

			HttpGet httpget = new HttpGet("https://localhost:8443/myDemo/Ajax/serivceJ.action");

			System.out.println("executing request" + httpget.getRequestLine());

			CloseableHttpResponse response = httpclient.execute(httpget);

			try {

				HttpEntity entity = response.getEntity();

				System.out.println("----------------------------------------");

				System.out.println(response.getStatusLine());

				if (entity != null) {

					System.out.println("Response content length: " + entity.getContentLength());

					System.out.println(EntityUtils.toString(entity));

					EntityUtils.consume(entity);

				}

			} finally {

				response.close();

			}

		} catch (ParseException e) {

			e.printStackTrace();

		} catch (IOException e) {

			e.printStackTrace();

		} catch (KeyManagementException e) {

			e.printStackTrace();

		} catch (NoSuchAlgorithmException e) {

			e.printStackTrace();

		} catch (KeyStoreException e) {

			e.printStackTrace();

		} finally {

			if (httpclient != null) {

				try {

					httpclient.close();

				} catch (IOException e) {

					e.printStackTrace();

				}

			}

		}

	}

	/**

	 * post方式提交表单（模拟用户登录请求）

	 */

	public void postForm() {

		// 创建默认的httpClient实例.

		CloseableHttpClient httpclient = HttpClients.createDefault();

		// 创建httppost

		HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");

		// 创建参数队列

		List<namevaluepair> formparams = new ArrayList<namevaluepair>();

		formparams.add(new BasicNameValuePair("username", "admin"));

		formparams.add(new BasicNameValuePair("password", "123456"));

		UrlEncodedFormEntity uefEntity;

		try {

			uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");

			httppost.setEntity(uefEntity);

			System.out.println("executing request " + httppost.getURI());

			CloseableHttpResponse response = httpclient.execute(httppost);

			try {

				HttpEntity entity = response.getEntity();

				if (entity != null) {

					System.out.println("--------------------------------------");

					System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));

					System.out.println("--------------------------------------");

				}

			} finally {

				response.close();

			}

		} catch (ClientProtocolException e) {

			e.printStackTrace();

		} catch (UnsupportedEncodingException e1) {

			e1.printStackTrace();

		} catch (IOException e) {

			e.printStackTrace();

		} finally {

			// 关闭连接,释放资源

			try {

				httpclient.close();

			} catch (IOException e) {

				e.printStackTrace();

			}

		}

	}

	/**

	 * 发送 post请求访问本地应用并根据传递参数不同返回不同结果

	 */

	public void post() {

		// 创建默认的httpClient实例.

		CloseableHttpClient httpclient = HttpClients.createDefault();

		// 创建httppost

		HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceJ.action");

		// 创建参数队列

		List<namevaluepair> formparams = new ArrayList<namevaluepair>();

		formparams.add(new BasicNameValuePair("type", "house"));

		UrlEncodedFormEntity uefEntity;

		try {

			uefEntity = new UrlEncodedFormEntity(formparams, "UTF-8");

			httppost.setEntity(uefEntity);

			System.out.println("executing request " + httppost.getURI());

			CloseableHttpResponse response = httpclient.execute(httppost);

			try {

				HttpEntity entity = response.getEntity();

				if (entity != null) {

					System.out.println("--------------------------------------");

					System.out.println("Response content: " + EntityUtils.toString(entity, "UTF-8"));

					System.out.println("--------------------------------------");

				}

			} finally {

				response.close();

			}

		} catch (ClientProtocolException e) {

			e.printStackTrace();

		} catch (UnsupportedEncodingException e1) {

			e1.printStackTrace();

		} catch (IOException e) {

			e.printStackTrace();

		} finally {

			// 关闭连接,释放资源

			try {

				httpclient.close();

			} catch (IOException e) {

				e.printStackTrace();

			}

		}

	}

	/**

	 * 发送 get请求

	 */

	public void get() {

		CloseableHttpClient httpclient = HttpClients.createDefault();

		try {

			// 创建httpget.

			HttpGet httpget = new HttpGet("http://www.baidu.com/");

			System.out.println("executing request " + httpget.getURI());

			// 执行get请求.

			CloseableHttpResponse response = httpclient.execute(httpget);

			try {

				// 获取响应实体

				HttpEntity entity = response.getEntity();

				System.out.println("--------------------------------------");

				// 打印响应状态

				System.out.println(response.getStatusLine());

				if (entity != null) {

					// 打印响应内容长度

					System.out.println("Response content length: " + entity.getContentLength());

					// 打印响应内容

					System.out.println("Response content: " + EntityUtils.toString(entity));

				}

				System.out.println("------------------------------------");

			} finally {

				response.close();

			}

		} catch (ClientProtocolException e) {

			e.printStackTrace();

		} catch (ParseException e) {

			e.printStackTrace();

		} catch (IOException e) {

			e.printStackTrace();

		} finally {

			// 关闭连接,释放资源

			try {

				httpclient.close();

			} catch (IOException e) {

				e.printStackTrace();

			}

		}

	}

	/**

	 * 上传文件

	 */

	public void upload() {

		CloseableHttpClient httpclient = HttpClients.createDefault();

		try {

			HttpPost httppost = new HttpPost("http://localhost:8080/myDemo/Ajax/serivceFile.action");

			FileBody bin = new FileBody(new File("F:\\image\\sendpix0.jpg"));

			StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN);

			HttpEntity reqEntity = MultipartEntityBuilder.create().addPart("bin", bin).addPart("comment", comment).build();

			httppost.setEntity(reqEntity);

			System.out.println("executing request " + httppost.getRequestLine());

			CloseableHttpResponse response = httpclient.execute(httppost);

			try {

				System.out.println("----------------------------------------");

				System.out.println(response.getStatusLine());

				HttpEntity resEntity = response.getEntity();

				if (resEntity != null) {

					System.out.println("Response content length: " + resEntity.getContentLength());

				}

				EntityUtils.consume(resEntity);

			} finally {

				response.close();

			}

		} catch (ClientProtocolException e) {

			e.printStackTrace();

		} catch (IOException e) {

			e.printStackTrace();

		} finally {

			try {

				httpclient.close();

			} catch (IOException e) {

				e.printStackTrace();

			}

		}

	}

}</namevaluepair></namevaluepair></namevaluepair></namevaluepair>

本实例是采用HttpClient4.3最新版本。该版本与之前的代码写法风格相差较大，大家多留意下。

httpclient其他功能

1、Java使用HttpURLConnection上传文件--http://blog.csdn.net/wangpeng047/article/details/38303865

2、Java如何获取Content-Type的文件类型Mime Type--http://blog.csdn.net/wangpeng047/article/details/38302395

转自http://blog.csdn.net/wangpeng047/article/details/19624529

巴特西

HttpClient（转载）

一、简介

二、特性

三、使用方法

四、实例

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