Apache HttpClient - 使用代理

代理服务器是客户端和互联网之间的中间服务器。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，您可以通过代理发送 HTTP 请求。请按照以下步骤操作：

步骤 1 - 创建 HttpHost 对象

通过传递一个字符串参数（表示需要从中发送请求的代理主机名称）到 org.apache.http 包的 HttpHost 类的构造函数来实例化该类。

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

以同样的方式，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 HttpRoutePlanner 对象

HttpRoutePlanner 接口计算到指定主机的路由。通过实例化 DefaultProxyRoutePlanner 类（该接口的一个实现）来创建此接口的对象。将其构造函数的参数设置为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，并使用 setRoutePlanner() 方法将上面创建的路由规划器设置为该对象。

//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 HttpGetobject

通过实例化 HttpGet 类创建一个 HTTP GET 请求。

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

步骤 6 - 执行请求

execute() 方法的其中一个变体接受 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。在本例中，我们通过 localhost 向 google.com 发送 HTTP GET 请求。我们打印了响应的标头和响应的主体。

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

执行上述程序后，将生成以下输出：

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>

打印页面