HttpClient 在Java项目中的使用详解

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:

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。