Apache HttpClient教程

HttpClient使用代理

代理服务器是客户端和Internet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，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目标

通过将表示代理主机名称的字符串参数(从中需要发送请求)传递给其构造函数来实例化org.apache.http包的HttpHost类。

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

以同样的方式，创建另一个HttpHost对象来表示需要向其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(此接口的实现)来创建此接口的对象。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径规划器。

//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("/");

第6步 - 执行请求
execute()方法的一个变体接受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。在此示例中，通过localhost向google.com发送HTTP GET请求。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));
      }
   }
}

执行上面示例代码，得到以下结果：

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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