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>