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