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，

 1 package proxy;
 2 
 3 import java.io.IOException;
 4 import java.io.PrintStream;
 5 import java.net.InetSocketAddress;
 6 import java.net.MalformedURLException;
 7 import java.net.Proxy;
 8 import java.net.URL;
 9 import java.net.URLConnection;
10 import java.util.Scanner;
11 
12 public class ProxyTest {
13     final String PROXY_ADDR = "172.20.230.5";
14     final int PROXY_PORT = 3128;
15     String urlStr = "http://www.baidu.com";
16     //String urlStr = "http://www.crazyit.org";
17     
18     public void init() throws IOException {
19         URL url = new URL(urlStr);
20         Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(PROXY_ADDR, PROXY_PORT));
21         //使用代理服务器打开链接
22         URLConnection conn = url.openConnection(proxy);
23         //URLConnection conn = url.openConnection();
24         conn.setConnectTimeout(5000);
25         try {
26             Scanner scan = new Scanner(conn.getInputStream());
27             PrintStream ps = new PrintStream("index.html");
28             while (scan.hasNextLine()) {
29                 String line = scan.nextLine();
30                 System.out.println(line);
31                 ps.println(line);
32             }
33         } catch (IOException e) {
34             e.printStackTrace();
35         }
36     }
37     
38     public static void main(String[] args) throws IOException {
39         new ProxyTest().init();
40     }
41 }

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，

 1 package proxy;
 2 
 3 import java.io.IOException;
 4 import java.io.PrintStream;
 5 import java.net.InetSocketAddress;
 6 import java.net.MalformedURLException;
 7 import java.net.Proxy;
 8 import java.net.ProxySelector;
 9 import java.net.SocketAddress;
10 import java.net.URI;
11 import java.net.URL;
12 import java.net.URLConnection;
13 import java.util.ArrayList;
14 import java.util.List;
15 import java.util.Scanner;
16 
17 public class ProxyTest {
18     final String PROXY_ADDR = "172.20.230.5";
19     final int PROXY_PORT = 3128;
20     String urlStr = "http://www.baidu.com";
21     //String urlStr = "http://www.crazyit.org";
22     
23     public void init() throws IOException {
24         ProxySelector.setDefault(new ProxySelector(){
25 
26             @Override
27             public void connectFailed(URI arg0, SocketAddress arg1,
28                     IOException arg2) {
29                 System.out.println("无法连接到服务器");
30                 
31             }
32 
33             @Override
34             public List<Proxy> select(URI uri) {
35                 List<Proxy> result = new ArrayList<>();
36                 result.add(new Proxy(Proxy.Type.HTTP, new InetSocketAddress(PROXY_ADDR, PROXY_PORT)));
37                 return result;
38             }
39             
40         });
41         
42         URL url = new URL(urlStr);
43         //使用代理服务器打开链接
44         URLConnection conn = url.openConnection();
45         conn.setConnectTimeout(5000);
46         try {
47             Scanner scan = new Scanner(conn.getInputStream());
48             PrintStream ps = new PrintStream("index.html");
49             while (scan.hasNextLine()) {
50                 String line = scan.nextLine();
51                 System.out.println(line);
52                 ps.println(line);
53             }
54         } catch (IOException e) {
55             e.printStackTrace();
56         }
57     }
58     
59     public static void main(String[] args) throws IOException {
60         new ProxyTest().init();
61     }
62 }

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