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

public class TcpEchoServer {
   private int port;

   public static void main(String[] args) {
      int port;
      
      if (args.length < 1) {
         (new TcpEchoServer()).go();
      } else {
         try {
            port = Integer.parseInt(args[0]);
            (new TcpEchoServer(port)).go();
         } catch(NumberFormatException ex) {
            System.out.println("Usage: TcpEchoServer [port]");
         }
      }
   }

   public TcpEchoServer() {
      this(7);
   }

   public TcpEchoServer(int port) {
      super();
      this.port = port;
   }

   public void go() {
      ServerSocket   echoSocket;
      Socket         clientSocket;
      
      try {
         echoSocket = new ServerSocket(port);
         System.out.println("Waiting for connections on port " + port + " ...");

         try {
            while (true) {
               clientSocket = echoSocket.accept();

               System.out.println("Connection from " +
                  clientSocket.getInetAddress() + " accepted.");

               (new ClientThread(clientSocket)).start();
            }
         } finally {
            echoSocket.close();
         }
         
      } catch(Exception ex) {
         System.out.println(ex);
      }

      System.exit(0);
   }

   class ClientThread extends Thread {
      Socket clientSocket;
   
      public ClientThread(Socket clientSocket) {
         super();
         this.clientSocket = clientSocket;
      }
   
      public void run() {
         OutputStream  out;
         InputStream   in;
         byte[]        inBuffer = new byte[1];
         int           bytesRead;

         try {
            in = clientSocket.getInputStream();
            out = clientSocket.getOutputStream();

            try {
               while (true) {
                  bytesRead = in.read(inBuffer);

                  // If EOF, then socket was closed by client, so break.

                  if (bytesRead == -1) {
                     break;
                  }
            
                  out.write(inBuffer);
               }
            } finally {
               clientSocket.close();

            }
         } catch(Exception ex) {
            System.out.println(ex);
         }

         System.out.println("Connection from " +
            clientSocket.getInetAddress() + " terminated.");
      }

   } // end ClientThread

} // end TcpEchoServer