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("");
      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("");
    // 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("");
    // 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("");
      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("");
      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。