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  Apache HttpClient - 使用代理

  • 简述

    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 -

  • 第 1 步 - 创建一个 HttpHost 对象

    通过传递代表代理名称的字符串参数来实例化 org.apache.http 包的 HttpHost 类主机，（您需要从中发送请求）到其构造函数。 
    
//为代理创建一个HttpHost对象
HttpHost proxyHost = new HttpHost("localhost");
    同理，再创建一个HttpHost对象，代表需要发送请求的目标主机。 
    
//Creating an HttpHost object for target
HttpHost targetHost = new HttpHost("google.com");

  • 第 2 步 - 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);

  • 第 3 步 - 将路线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线规划器，使用 setRoutePlanner() 方法。 
    
//Setting the route planner to the HttpClientBuilder object
HttpClientBuilder clientBuilder = HttpClients.custom();
clientBuilder = clientBuilder.setRoutePlanner(routePlanner);

  • 第 4 步 - 构建 CloseableHttpClient 对象

    通过调用 build() 方法构建 CloseableHttpClient 对象。 
    
//构建一个CloseableHttpClient
CloseableHttpClient httpClient = clientBuilder.build();

  • 第 5 步 - 创建一个 HttpGetobject

    通过实例化 HttpGet 类创建一个 HTTP GET 请求。 
    
//创建一个HttpGet对象
HttpGet httpGet = new HttpGet("/");

  • 第 6 步 - 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 - 
    
//执行Get请求
HttpResponse httpResponse = httpclient.execute(targetHost, httpGet);

  • 示例

    以下示例演示如何通过代理向服务器发送 HTTP 请求。在这个 例如，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头和响应的正文。 
    
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

    在执行时，上面的程序生成以下输出 - 
    
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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