Java/Network Protocol/Proxy Server

A simple proxy server

 
import java.io.*;
import java.net.*;
public class SimpleProxyServer {
  public static void main(String[] args) throws IOException {
    try {
      String host = "your Proxy Server";
      int remoteport = 100;
      int localport = 111;
      // Print a start-up message
      System.out.println("Starting proxy for " + host + ":" + remoteport
          + " on port " + localport);
      // And start running the server
      runServer(host, remoteport, localport); // never returns
    } catch (Exception e) {
      System.err.println(e);
    }
  }
  /**
   * runs a single-threaded proxy server on
   * the specified local port. It never returns.
   */
  public static void runServer(String host, int remoteport, int localport)
      throws IOException {
    // Create a ServerSocket to listen for connections with
    ServerSocket ss = new ServerSocket(localport);
    final byte[] request = new byte[1024];
    byte[] reply = new byte[4096];
    while (true) {
      Socket client = null, server = null;
      try {
        // Wait for a connection on the local port
        client = ss.accept();
        final InputStream streamFromClient = client.getInputStream();
        final OutputStream streamToClient = client.getOutputStream();
        // Make a connection to the real server.
        // If we cannot connect to the server, send an error to the
        // client, disconnect, and continue waiting for connections.
        try {
          server = new Socket(host, remoteport);
        } catch (IOException e) {
          PrintWriter out = new PrintWriter(streamToClient);
          out.print("Proxy server cannot connect to " + host + ":"
              + remoteport + ":\n" + e + "\n");
          out.flush();
          client.close();
          continue;
        }
        // Get server streams.
        final InputStream streamFromServer = server.getInputStream();
        final OutputStream streamToServer = server.getOutputStream();
        // a thread to read the client"s requests and pass them
        // to the server. A separate thread for asynchronous.
        Thread t = new Thread() {
          public void run() {
            int bytesRead;
            try {
              while ((bytesRead = streamFromClient.read(request)) != -1) {
                streamToServer.write(request, 0, bytesRead);
                streamToServer.flush();
              }
            } catch (IOException e) {
            }
            // the client closed the connection to us, so close our
            // connection to the server.
            try {
              streamToServer.close();
            } catch (IOException e) {
            }
          }
        };
        // Start the client-to-server request thread running
        t.start();
        // Read the server"s responses
        // and pass them back to the client.
        int bytesRead;
        try {
          while ((bytesRead = streamFromServer.read(reply)) != -1) {
            streamToClient.write(reply, 0, bytesRead);
            streamToClient.flush();
          }
        } catch (IOException e) {
        }
        // The server closed its connection to us, so we close our
        // connection to our client.
        streamToClient.close();
      } catch (IOException e) {
        System.err.println(e);
      } finally {
        try {
          if (server != null)
            server.close();
          if (client != null)
            client.close();
        } catch (IOException e) {
        }
      }
    }
  }
}

Install Proxy Selector

 
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Proxy;
import java.net.ProxySelector;
import java.net.SocketAddress;
import java.net.URI;
import java.util.ArrayList;
import java.util.List;
public class Utils {
  private static void installProxySelector(final String hostName, final int portNum) {
    ProxySelector.setDefault(new ProxySelector() {
      public List select(URI uri) {
        List list = new ArrayList();
        list.add(new Proxy(Proxy.Type.HTTP, new InetSocketAddress(hostName, portNum)));
        return list;
      }
      public void connectFailed(URI uri, SocketAddress sa, IOException ioe) {
      }
    });
  }
}