Passing a value to the main program from a channel handler in netty

Question

I am writing a client using netty for handling custom protocol. I have defined a handler which extends SimpleChannelInboundHandler which handles both sending and receiving message.

public  class ClientHandler extends SimpleChannelInboundHandler {
    @Override
    protected void channelRead0(ChannelHandlerContext channelHandlerContext, Object o) throws Exception {
        log.info("Client received: " + ((ByteBuf)o).toString(CharsetUtil.UTF_8));
        System.out.println("Client received: " + ((ByteBuf)o).toString(CharsetUtil.UTF_8));
    }

    @Override
    public void channelActive(ChannelHandlerContext channelHandlerContext){
        log.info("Client sent: $"+ new MessageRequest().toString() +"$");
        channelHandlerContext.writeAndFlush(Unpooled.copiedBuffer((new MessageRequest().toString()), CharsetUtil.UTF_8));
    }


    @Override
    public void exceptionCaught(ChannelHandlerContext channelHandlerContext, Throwable cause){
        cause.printStackTrace();
        channelHandlerContext.close();
    }
}

This handler is able to print the response to the console. But since I am writing an client which will be used by another service, I need to send the response to the service which is calling my client.

Kindly help me in sending the response received to the calling service.

It's asynchronous, so you'll need to use some form of callback mechanism to "return" a value to the service. But you'll need to chose how it should work, could be for example a simple [callback interface](https://stackoverflow.com/questions/18279302/how-do-i-perform-a-java-callback-between-classes), an [elaborate event system](https://github.com/iluwatar/java-design-patterns/tree/master/event-driven-architecture), [EventBus](https://github.com/google/guava/wiki/EventBusExplained) or even something like [RxJava](https://stackoverflow.com/q/42118782/995891). — zapl, Oct 17 '18 at 16:06

Riyafa Abdul Hameed · Accepted Answer · 2018-10-18T02:12:31.263

0

You can store the reference of your listening service in your ClientHandler class and call a setMessage method of the service class to give it the message from the channelRead0 method of your handler.

A better approach would be to use the Observer pattern

edited Oct 18 '18 at 02:12

answered Oct 17 '18 at 15:45

Riyafa Abdul Hameed

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Passing a value to the main program from a channel handler in netty

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