Exemplo de Server usando Socket (Simples)

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

public class Server
{

	static public void main( String args[] )
	{
		try
		{
			new Server();
		}
		catch( Exception e )
		{
			System.out.println( e.getMessage() );
			e.printStackTrace();
		}
	}

	Server() throws Exception
	{
		int session = 1;
		ServerSocket ss = new ServerSocket(8765);
		while ( true )
		{
			System.out.println( "Aguardando porta 8765" );
			Socket s = ss.accept();
			System.out.println( "Conexao efetuada" );
			AtendeClient cs = new AtendeClient(s,session++);
			Thread t = new Thread(cs);
			t.start();
		}
	}
}

class AtendeClient implements Runnable {

	Socket s;
	InputStream is;
	OutputStream os;
	int session;

	AtendeClient( Socket s, int session ) throws Exception
	{
		this.s = s;
		System.out.println( "Iniciando sessao" );
		this.is = s.getInputStream();
		this.os = s.getOutputStream();
		this.session = session;
	}

	public void run()
	{
		byte buffer[] = new byte[31];
		try
		{
			while ( true ) {
				is.read( buffer );
				System.out.println( "Dados recebidos client ("+session+")=>"+( new String(buffer) ) );
				os.write( buffer );
				os.flush();
			}
		}
		catch( Exception e )
		{
			System.out.println( e.getMessage() );
		}
	}
}