Proxy.java

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

public class Proxy {
    int local_port;
    int destiny_port;
    String destiny_url;

    ServerSocket server;

    Socket proxy;
    Socket destiny;

    InputStream from_destiny;
    OutputStream to_destiny; 

    InputStream from_local;
    OutputStream to_local; 

    //constructor
    Proxy() {
    }

    public static void main(String[] args){
        Proxy client = new Proxy();
        client.startProxy(args);
    }

    private void startProxy(String[] args){
        if(args.length != 3){
            System.out.println("Usage: java Proxy local_port destiny_port destiny_url");
            return;
        }

        try{
            //get the ports and destiny from command line
            local_port = Integer.parseInt(args[0]);
            destiny_port = Integer.parseInt(args[1]);
            destiny_url = args[2];
        }catch (Exception e) {
            System.out.println(e);
        }

        //open a new socket 
        try{
            server = new ServerSocket(local_port);
        }catch(IOException e){
            System.out.println(e);
            return;
        }

        //create space to data
        byte[] input_data = new byte[4096];
        byte[] output_data = new byte[4096];

        while(true){
            try{
                proxy = server.accept();
            }catch(IOException e){
                System.out.println(e);
                return;
            }

            try{
                from_local = proxy.getInputStream();
                to_local = proxy.getOutputStream();
            }catch(IOException e){
                System.out.println(e);
                return;
            }

            try{
                destiny = new Socket(destiny_url, destiny_port);
            }catch (Exception e) {
                System.out.println(e);
                return;
            }


            try{
                from_destiny = destiny.getInputStream();
                to_destiny = destiny.getOutputStream();

                Thread sync = new Thread() {
                    public void run() {
                        int reader;
                        try {
                            while((reader = from_local.read(input_data)) != -1) {
                                to_destiny.write(input_data, 0, reader);
                                to_destiny.flush();
                            }

                            to_destiny.close();
                        } catch (IOException e) {}
                    }
                };

                sync.start();  

                int writer;
                while((writer = from_destiny.read(output_data)) != -1) {
                    to_local.write(output_data, 0, writer);
                    to_local.flush();
                }

                to_local.close();

                proxy.close();
                destiny.close();
            }catch(IOException e){
                System.out.println(e);
                return;
            }
        }
    }
}