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The Netty Project 3.2 User Guide

The Proven Approach

to Rapid Network

Application Development

3.2.1.Final, r2319

ii

Preface .............................................................................................................................. iii

1. The Problem ........................................................................................................... iii

2. The Solution ........................................................................................................... iii

1.6. Writing a Time Client ............................................................................................. 7

1.7. Dealing with a Stream-based Transport ...................................................................... 8

1.7.1. One Small Caveat of Socket Buffer ................................................................. 8

1.7.2. The First Solution ........................................................................................ 9

1.7.3. The Second Solution ................................................................................... 10

1.8. Speaking in POJO instead of ChannelBuffer .............................................................. 12

1.9. Shutting Down Your Application ............................................................................. 14

1.10. Summary ........................................................................................................... 17

2. Architectural Overview .................................................................................................. 18

2.1. Rich Buffer Data Structure ..................................................................................... 18

2.4.4. Google Protocol Buffer Integration ................................................................ 21

2.5. Summary ............................................................................................................ 21

Preface

1. The Problem

Nowadays we use general purpose applications or libraries to communicate with each other. For example,

we often use an HTTP client library to retrieve information from a web server and to invoke a remote

procedure call via web services.

However, a general purpose protocol or its implementation sometimes does not scale very well. It is like

we don't use a general purpose HTTP server to exchange huge files, e-mail messages, and near-realtime

messages such as financial information and multiplayer game data. What's required is a highly optimized

2. The Solution

The Netty project is an effort to provide an asynchronous event-driven network application framework and

tooling for the rapid development of maintainable high-performance high-scalability protocol servers and

clients.

In other words, Netty is a NIO client server framework which enables quick and easy development of

network applications such as protocol servers and clients. It greatly simplifies and streamlines network

programming such as TCP and UDP socket server development.

'Quick and easy' does not mean that a resulting application will suffer from a maintainability or a

performance issue. Netty has been designed carefully with the experiences earned from the implementation

of a lot of protocols such as FTP, SMTP, HTTP, and various binary and text-based legacy protocols. As

this philosophy will make your life much easier as you read this guide and play with Netty.

Chapter 1.

1

Getting Started

This chapter tours around the core constructs of Netty with simple examples to let you get started quickly.

You will be able to write a client and a server on top of Netty right away when you are at the end of this

chapter.

If you prefer top-down approach in learning something, you might want to start from Chapter 2,

Architectural Overview and get back here.

1.1. Before Getting Started

The minimum requirements to run the examples which are introduced in this chapter are only two; the latest

have a good idea to improve the documentation.

1.2. Writing a Discard Server

The most simplistic protocol in the world is not 'Hello, World!' but DISCARD. It's a protocol which discards

any received data without any response.

To implement the DISCARD protocol, the only thing you need to do is to ignore all received data. Let us

start straight from the handler implementation, which handles I/O events generated by Netty.

package org.jboss.netty.example.discard;

public class DiscardServerHandler extends SimpleChannelHandler {

@Override

public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {

ch.close();

}

}

2

So far so good. We have implemented the first half of the DISCARD server. What's left now is to write the

package org.jboss.netty.example.discard;

import java.net.InetSocketAddress;

import java.util.concurrent.Executors;

public class DiscardServer {

public static void main(String[] args) throws Exception {

ChannelFactory factory =

new NioServerSocketChannelFactory (

Executors.newCachedThreadPool(),

});

bootstrap.setOption("child.tcpNoDelay", true);

bootstrap.setOption("child.keepAlive", true);

bootstrap.bind(new InetSocketAddress(8080));

}

}