Simple Network Proxy

ProxyServer.java

import java.io.*;
import java.net.*;

public class ProxyServer
{
    /**
     * Thread to handle a single client connection
     * This way the server can handle other incoming requests
     */
    public static class ClientHandler extends Thread
    {
        Socket client;
        Socket server;
        
        public ClientHandler(Socket client,Socket server)
        {
            super("ClientHandler: "+client.getInetAddress()+"=>"+server.getInetAddress());
            this.client = client;
            this.server = server;            
        }

        public void run()
        {
            try {
                String address = client.getInetAddress().getHostAddress();                
                System.out.println("ClientHandler: Handling client from "+address);
                InputStream clientInput   = client.getInputStream();
                OutputStream clientOutput = client.getOutputStream();
                InputStream serverInput   = server.getInputStream();
                OutputStream serverOutput = server.getOutputStream();
                 
                IOPipe clientToServer = new IOPipe(clientInput,serverOutput);
                IOPipe serverToClient = new IOPipe(serverInput,clientOutput);
                clientToServer.start();
                serverToClient.start();
                clientToServer.join();
                serverToClient.join();
                System.out.println("ClientHandler: Connection to "+address+" is closed");
            }
            catch (Exception e) {
                e.printStackTrace();
            }
            finally {
                try { client.close(); } catch (IOException e1) {}
                try { server.close(); } catch (IOException e2) {}
            }            
        }        
    }
    
    /*
     * Thread to pipe one socket's input another's output so that the IO is non-blocking
     */
    public static class IOPipe extends Thread
    {
        InputStream input;
        OutputStream output;
        
        public IOPipe(InputStream input, OutputStream output) {
            super("IOPipe");
            this.input = input;
            this.output = output;
        }
        
        // Pipe the input to the output
        public void run()
        {
            int bytesRead = 0;
            byte buffer[] = new byte[64000];
            try {
                while ((bytesRead = input.read(buffer)) > 0) {
                    output.write(buffer,0,bytesRead);
                }
            }
            catch (Exception e) {
                e.printStackTrace();
            }
            /*
            finally {
                try { output.close(); } catch (IOException e1) {}
                try { input.close(); } catch (IOException e2) {}
            }
            */
        }
    }
    
    
    public static void main(String args[]) 
        throws Exception
    {
        ServerSocket serverSocket = null;
        if (args.length < 4) {
            System.out.println("Usage: java ProxyServer [localhost] [localport] [remotehost] [remoteport]");
            System.exit(-1);          
        }
        
        String localhost = args[0];
        int localport = Integer.parseInt(args[1]);
        String remotehost = args[2];
        int remoteport = Integer.parseInt(args[3]);
        
        try {
            serverSocket = new ServerSocket(localport);
        } catch (IOException e) {
            System.out.println("Could not listen on port: "+localport+": "+e.toString());
            System.exit(-1);
        }
        
        System.out.println("ProxyServer: Waiting for connections ...");
        Socket clientSocket = null;
        try {
            while (true) {
                clientSocket = serverSocket.accept();
                String address = clientSocket.getInetAddress().getHostAddress();
                System.out.println("ProxyServer: Got a client from "+address);
                Socket remoteSocket = new Socket(remotehost,remoteport);
                ClientHandler handler = new ClientHandler(clientSocket,remoteSocket);
                handler.start();
            }
        } catch (IOException e) {
            System.out.println(e.toString());
            System.exit(-1);
        }        
        serverSocket.close();
    }
}