Apache HttpClient - 使用代理

代理伺服器是客戶端和網際網路之間的中間伺服器。代理伺服器提供以下基本功能：

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使用 HttpClient 庫，您可以透過代理傳送 HTTP 請求。請按照以下步驟操作：

步驟 1 - 建立 HttpHost 物件

透過傳遞一個字串引數（表示需要從中傳送請求的代理主機名稱）到 org.apache.http 包的 HttpHost 類的建構函式來例項化該類。

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

以同樣的方式，建立另一個 HttpHost 物件來表示需要傳送請求的目標主機。

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

步驟 2 - 建立 HttpRoutePlanner 物件

HttpRoutePlanner 介面計算到指定主機的路由。透過例項化 DefaultProxyRoutePlanner 類（該介面的一個實現）來建立此介面的物件。將其建構函式的引數設定為上面建立的代理主機：

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

步驟 3 - 將路由規劃器設定為客戶端構建器

使用 HttpClients 類的 custom() 方法建立一個 HttpClientBuilder 物件，並使用 setRoutePlanner() 方法將上面建立的路由規劃器設定為該物件。

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

clientBuilder = clientBuilder.setRoutePlanner(routePlanner);

步驟 4 - 構建 CloseableHttpClient 物件

透過呼叫 build() 方法構建 CloseableHttpClient 物件。

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

步驟 5 - 建立 HttpGetobject

透過例項化 HttpGet 類建立一個 HTTP GET 請求。

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

步驟 6 - 執行請求

execute() 方法的其中一個變體接受 HttpHost 和 HttpRequest 物件並執行請求。使用此方法執行請求：

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

示例

以下示例演示瞭如何透過代理向伺服器傳送 HTTP 請求。在本例中，我們透過 localhost 向 google.com 傳送 HTTP GET 請求。我們列印了響應的標頭和響應的主體。

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));
      }
   }
}

輸出

執行上述程式後，將生成以下輸出：

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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