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copied!<p>If you are working with NIO, I would also suggest to use a Framework. I have been working with <a href="http://mina.apache.org/" rel="nofollow noreferrer">Apache Mina</a> and I would recommend it.</p> <p>As to the blocking IO, essentially you will need a Listener Thread that accepts incoming connections and spawns additional threads that will handle each connection. Here is an example of such a Listener code, as originally contributed to the Apache Felix Project. If you look for the complete but modified version, you can <a href="http://svn.apache.org/viewvc/felix/trunk/shell.remote/src/main/java/org/apache/felix/shell/remote/" rel="nofollow noreferrer">browse the source here</a>.</p> <p>e.g.</p> <pre><code> /* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.felix.shell.remote; import java.io.IOException; import java.io.PrintStream; import java.net.ServerSocket; import java.net.Socket; import java.net.SocketException; /** * Implements a simple listener that will accept a single connection. * <p/> * * @author Dieter Wimberger (wimpi) */ class Listener { private int m_Port; private Thread m_ListenerThread; private boolean m_Stop = false; private ServerSocket m_ServerSocket; private AtomicInteger m_UseCounter; private int m_MaxConnections; /** * Activates this listener on a listener thread (telnetconsole.Listener). */ public void activate() { //configure from system property try { m_Port = Integer.parseInt( System.getProperty( "osgi.shell.telnet.port", "6666" ) ); } catch ( NumberFormatException ex ) { Activator.getServices().error( "Listener::activate()", ex ); } try { m_MaxConnections = Integer.parseInt( System.getProperty( "osgi.shell.telnet.maxconn", "2" ) ); } catch ( NumberFormatException ex ) { Activator.getServices().error( "Listener::activate()", ex ); } m_UseCounter = new AtomicInteger( 0 ); m_ListenerThread = new Thread( new Acceptor(), "telnetconsole.Listener" ); m_ListenerThread.start(); }//activate /** * Deactivates this listener. * <p/> * The listener's socket will be closed, which should cause an interrupt in the * listener thread and allow for it to return. The calling thread joins the listener * thread until it returns (to ensure a clean stop). */ public void deactivate() { try { m_Stop = true; //wait for the listener thread m_ServerSocket.close(); m_ListenerThread.join(); } catch ( Exception ex ) { Activator.getServices().error( "Listener::deactivate()", ex ); } }//deactivate /** * Class that implements the listener's accept logic as a <tt>Runnable</tt>. */ private class Acceptor implements Runnable { /** * Listens constantly to a server socket and handles incoming connections. * One connection will be accepted and routed into the shell, all others will * be notified and closed. * <p/> * The mechanism that should allow the thread to unblock from the ServerSocket.accept() call * is currently closing the ServerSocket from another thread. When the stop flag is set, * this should cause the thread to return and stop. */ public void run() { try { /* A server socket is opened with a connectivity queue of a size specified in int floodProtection. Concurrent login handling under normal circumstances should be handled properly, but denial of service attacks via massive parallel program logins should be prevented with this. */ m_ServerSocket = new ServerSocket( m_Port, 1 ); do { try { Socket s = m_ServerSocket.accept(); if ( m_UseCounter.get() >= m_MaxConnections ) { //reject with message PrintStream out = new PrintStream( s.getOutputStream() ); out.print( INUSE_MESSAGE ); out.flush(); //close out.close(); s.close(); } else { m_UseCounter.increment(); //run on the connection thread Thread connectionThread = new Thread( new Shell( s, m_UseCounter ) ); connectionThread.start(); } } catch ( SocketException ex ) { } } while ( !m_Stop ); } catch ( IOException e ) { Activator.getServices().error( "Listener.Acceptor::activate()", e ); } }//run }//inner class Acceptor private static final String INUSE_MESSAGE = "Connection refused.\r\n" + "All possible connections are currently being used.\r\n"; }//class Listener </code></pre> <p>You can find other examples <a href="http://jamod.cvs.sourceforge.net/viewvc/jamod/jamod/src/net/wimpi/modbus/net/ModbusTCPListener.java?revision=1.4&view=markup" rel="nofollow noreferrer">here</a> and <a href="http://telnetd.svn.sourceforge.net/viewvc/telnetd/osgi/trunk/src/java/net/wimpi/telnetd/net/" rel="nofollow noreferrer">here</a>.</p> <p>Note that the advantage of NIO over the blocking model comes into play when you have more load. From a certain point on, the amount of extra work for Thread creation, management and context switching will limit your system performance. </p>

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