JAVA基礎知識之網絡編程——-使用Proxy創建連接

在前面的HTTP網絡通信的例子中，使用了URLConnection conn = url.openConnection();連接網絡，

如果改用URLConnection conn = url.openConnection(proxy);方式，傳入一個proxy對象，設置好代理IP和端口，則可以實現代理連接，

下面是一個簡單例子，

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));
        //使用代理服務器打開鏈接
        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();
    }
}

實現自動代理

在上面的例子中，每次用url對象open一個connection的時候，都需要顯示地傳入一個proxy對象才行。

而實際上可以在connection之前，做一個默認代理設置，這樣以后再openConnection的時候，就不需要顯示傳入proxy對象了。

做默認代理設置需要重寫ProxySelector的select方法，返回代理IP和端口列表，具體實現如下，

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("無法連接到服務器");
                
            }

            @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))); 37                 return result;
            }
            
        });
        
        URL url = new URL(urlStr);
        //使用代理服務器打開鏈接
        URLConnection conn = url.openConnection(); 45         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打開鏈接時就能像普通連接那樣url.openConnection();了