HttpClient使用详解

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 formparams = new ArrayList();
         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 formparams = new ArrayList();
         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();
             }
         }
     }
 }

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。

本文转载自：http://blog.csdn.net/wangpeng047/article/details/19624529