Netty detect when client network changed and closed -> PING, PONG

This guide is for the users who are already used to using netty


Actually I tried to make chatting program with Netty
I was very happy to know netty and it seems to be very good for speed and connections

but I faced with some problem
When Android Client side Stop application exit it Serverside relize that client is disconnected.
but when client change 4g to wifi client connection lost, however Serverside dosen't know about client lost.
noting happend.

so I google and found some good handler .
this is ping periodically .
and server side finally exactly know whether specific client is where alive or not.

=== Explain ==

idleStateHandler

readerIdleTime	an IdleStateEvent whose state is IdleState.READER_IDLE will be triggered when no read was performed for the specified period of time. Specify 0 to disable.
writerIdleTime	an IdleStateEvent whose state is IdleState.WRITER_IDLE will be triggered when no write was performed for the specified period of time. Specify 0 to disable.
allIdleTime	an IdleStateEvent whose state is IdleState.ALL_IDLE will be triggered when neither read nor write was performed for the specified period of time. Specify 0 to disable.

pipeline.addLast("idleStateHandler", new IdleStateHandler(60, 30, 0));        pipeline.addLast("myHandler", new MyHandler());

class MyHandler extends ChannelDuplexHandler {

    @Override

    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {

        if (evt instanceof IdleStateEvent) {

            IdleStateEvent e = (IdleStateEvent) evt;

            if (e.state() == IdleState.READER_IDLE) {

                System.out.println("reader ");

                System.out.println("reader ");

                System.out.println("reader ");

                System.out.println("reader ");

            ctx.close();

            } else if (e.state() == IdleState.WRITER_IDLE) {

                 try{

             ctx.channel().writeAndFlush("ping:"+ctx.channel().hashCode() );

                 }catch(Exception es){

                 es.printStackTrace();

                 }

             System.out.println("writer ");

                 System.out.println("writer ");

            }

        }

    }

}