JAVA基础知识之网络编程——-使用Proxy创建连接

在前面的HTTP网络通信的例子中，使用了URLConnection conn = url.openConnection();连接网络，

如果改用URLConnection conn = url.openConnection(proxy);方式，传入一个proxy对象，设置好代理IP和端口，则可以实现代理连接，

下面是一个简单例子，

 package proxy;

 import java.io.IOException;
 import java.io.PrintStream;
 import java.net.InetSocketAddress;
 import java.net.MalformedURLException;
 import java.net.Proxy;
 import java.net.URL;
 import java.net.URLConnection;
 import java.util.Scanner;

 public class ProxyTest {
     final String PROXY_ADDR = "172.20.230.5";
     final int PROXY_PORT = 3128;
     String urlStr = "http://www.baidu.com";
     //String urlStr = "http://www.crazyit.org";

     public void init() throws IOException {
         URL url = new URL(urlStr);
         Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(PROXY_ADDR, PROXY_PORT));
         //使用代理服务器打开链接
         URLConnection conn = url.openConnection(proxy);
         //URLConnection conn = url.openConnection();
         conn.setConnectTimeout(5000);
         try {
             Scanner scan = new Scanner(conn.getInputStream());
             PrintStream ps = new PrintStream("index.html");
             while (scan.hasNextLine()) {
                 String line = scan.nextLine();
                 System.out.println(line);
                 ps.println(line);
             }
         } catch (IOException e) {
             e.printStackTrace();
         }
     }

     public static void main(String[] args) throws IOException {
         new ProxyTest().init();
     }
 }

实现自动代理

在上面的例子中，每次用url对象open一个connection的时候，都需要显示地传入一个proxy对象才行。

而实际上可以在connection之前，做一个默认代理设置，这样以后再openConnection的时候，就不需要显示传入proxy对象了。

做默认代理设置需要重写ProxySelector的select方法，返回代理IP和端口列表，具体实现如下，

 package proxy;

 import java.io.IOException;
 import java.io.PrintStream;
 import java.net.InetSocketAddress;
 import java.net.MalformedURLException;
 import java.net.Proxy;
 import java.net.ProxySelector;
 import java.net.SocketAddress;
 import java.net.URI;
 import java.net.URL;
 import java.net.URLConnection;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Scanner;

 public class ProxyTest {
     final String PROXY_ADDR = "172.20.230.5";
     final int PROXY_PORT = 3128;
     String urlStr = "http://www.baidu.com";
     //String urlStr = "http://www.crazyit.org";

     public void init() throws IOException {
         ProxySelector.setDefault(new ProxySelector(){

             @Override
             public void connectFailed(URI arg0, SocketAddress arg1,
                     IOException arg2) {
                 System.out.println("无法连接到服务器");

             }

             @Override
             public List<Proxy> select(URI uri) {
                 List<Proxy> result = new ArrayList<>();
                 result.add(new Proxy(Proxy.Type.HTTP, new InetSocketAddress(PROXY_ADDR, PROXY_PORT)));
                 return result;
             }

         });

         URL url = new URL(urlStr);
         //使用代理服务器打开链接
         URLConnection conn = url.openConnection();
         conn.setConnectTimeout(5000);
         try {
             Scanner scan = new Scanner(conn.getInputStream());
             PrintStream ps = new PrintStream("index.html");
             while (scan.hasNextLine()) {
                 String line = scan.nextLine();
                 System.out.println(line);
                 ps.println(line);
             }
         } catch (IOException e) {
             e.printStackTrace();
         }
     }

     public static void main(String[] args) throws IOException {
         new ProxyTest().init();
     }
 }

可以看到使用代理之后，再用url打开链接时就能像普通连接那样url.openConnection();了