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，您可以使用代理发送 HTTP 请求。请按照以下步骤操作 -

第 1 步 - 创建 HttpHost 对象

通过将表示代理主机名称（您需要从中发送请求）的字符串参数传递给其构造函数，实例化org.apache.http包的HttpHost类。

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

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");

第 2 步 - 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（该接口的实现）来创建该接口的对象。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，并使用setRoutePlanner()方法为此对象设置上面创建的路由规划器。

//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。

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

第 5 步 - 创建 HttpGet 对象

通过实例化HttpGet类来创建 HTTP GET 请求。

//Creating an HttpGet object
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 -

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

例子

以下示例演示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>