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Apache HttpClient - 使用代理

代理服务器是客户端和互联网之间的中介服务器。 代理服务器提供以下基本功能 −

  • 防火墙和网络数据过滤

  • 网络连接共享

  • 数据缓存

使用 HttpClient 库，您可以使用代理发送 HTTP 请求。 按照下面给出的步骤 −

步骤 1 - 创建一个 HttpHost 对象

通过传递一个代表代理主机名称的字符串参数来实例化 org.apache.http 包的 HttpHost 类，（您需要从中请求 被发送）到它的构造函数。

//Creating an HttpHost object for proxy
HttpHost proxyHost = new HttpHost("localhost");

同样，创建另一个 HttpHost 对象来表示需要发送请求的目标主机。

//Creating an HttpHost object for target
HttpHost targetHost = new HttpHost("google.com");

步骤 2 - 创建一个 HttpRoutePlanner 对象

HttpRoutePlanner 接口计算到指定主机的路由。 通过实例化 DefaultProxyRoutePlanner 类来创建该接口的一个对象，该类是该接口的一个实现。 作为其构造函数的参数，传递上面创建的代理主机 −

//creating a RoutePlanner object
HttpRoutePlanner routePlanner = new DefaultProxyRoutePlanner(proxyhost);

步骤 3 - 将路由规划器设置为客户端构建器

使用 HttpClients 类的 custom() 方法，创建一个 HttpClientBuilder 对象，并为该对象设置上面创建的路由规划器 ，使用 setRoutePlanner() 方法。

//Setting the route planner to the HttpClientBuilder object
HttpClientBuilder clientBuilder = HttpClients.custom();

clientBuilder = clientBuilder.setRoutePlanner(routePlanner);

步骤 4 - 构建 CloseableHttpClient 对象

通过调用 build() 方法构建 CloseableHttpClient 对象。

//Building a CloseableHttpClient
CloseableHttpClient httpClient = clientBuilder.build();

步骤 5 - 创建一个 HttpGetobject

通过实例化 HttpGet 类来创建 HTTP GET 请求。

//Creating an HttpGet object
HttpGet httpGet = new HttpGet("/");

步骤 6 - 执行请求

execute() 方法的变体之一接受 HttpHost 和 HttpRequest 对象并执行请求。 使用此方法执行请求 −

//Executing the Get request
HttpResponse httpResponse = httpclient.execute(targetHost, httpGet);

示例

以下示例演示了如何通过代理向服务器发送 HTTP 请求。 在此示例中，我们通过 localhost 向 google.com 发送 HTTP GET 请求。 我们已经打印了响应的标题和响应的正文。

import org.apache.http.Header;
import org.apache.http.HttpEntity;
import org.apache.http.HttpHost;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.conn.routing.HttpRoutePlanner;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.DefaultProxyRoutePlanner;
import org.apache.http.util.EntityUtils;

public class RequestViaProxyExample {

   public static void main(String args[]) throws Exception{
 
      //Creating an HttpHost object for proxy
      HttpHost proxyhost = new HttpHost("localhost");

      //Creating an HttpHost object for target
      HttpHost targethost = new HttpHost("google.com");
 
      //creating a RoutePlanner object
      HttpRoutePlanner routePlanner = new DefaultProxyRoutePlanner(proxyhost);

      //Setting the route planner to the HttpClientBuilder object
      HttpClientBuilder clientBuilder = HttpClients.custom();
      clientBuilder = clientBuilder.setRoutePlanner(routePlanner);

      //Building a CloseableHttpClient
      CloseableHttpClient httpclient = clientBuilder.build();

      //Creating an HttpGet object
      HttpGet httpget = new HttpGet("/");

      //Executing the Get request
      HttpResponse httpresponse = httpclient.execute(targethost, httpget);

      //Printing the status line
      System.out.println(httpresponse.getStatusLine());

      //Printing all the headers of the response
      Header[] headers = httpresponse.getAllHeaders();
 
      for (int i = 0; i < headers.length; i++) {
         System.out.println(headers[i]);
      }
      
      //Printing the body of the response
      HttpEntity entity = httpresponse.getEntity();

      if (entity != null) {
         System.out.println(EntityUtils.toString(entity));
      }
   }
}

输出

执行时，上述程序生成以下输出 −

HTTP/1.1 200 OK
Date: Sun, 23 Dec 2018 10:21:47 GMT
Server: Apache/2.4.9 (Win64) PHP/5.5.13
Last-Modified: Tue, 24 Jun 2014 10:46:24 GMT
ETag: "2e-4fc92abc3c000"
Accept-Ranges: bytes
Content-Length: 46
Content-Type: text/html
<html><body><h1>It works!</h1></body></html>
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