Netty入门实例及分析

什么是netty？以下是官方文档的简单介绍：

The Netty project  is an effort to provide
an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and 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/IP
socket server.

以下写一个简单的实例：

1.client细节分析

ChannelFactory是创建一个通道（和一次详细的通信实体关联如网络套接字）的主要接口。比方NioServerSocketChannelFactory 会创建一个Channel，有基于NIO的服务套接字作为底层的通信实体。一旦一个新的通道创建。那么相应的ChannelPipeline就会開始处理相关的ChannelEvents。

 

NioClientSocketChannelFactory会创建一个client的基于NIO的SocketChannel。利用非堵塞IO模型来高效处理这些并发的连接。当中有两种类型的线程， boss thread 和 worker thread，每一个NioClientSocketChannelFactory
有一个boss thread。它主要是有请求要发出时试图进行一次连接。连接成功后，将这个连接的通道交付给一个worker thread。接下来这个worker thread 为一个或多个通道运行非堵塞的读写服务。

ClientBootstrap仅仅是一个辅助函数，不会分配或者管理不论什么资源，管理资源是由构造器中指定的ChannelFactory完毕的。所以从同一个ChannelFactory衍生出多个ClientBootstrap是能够的。从而为不同的Channel应用不同的设置。connect（）方法会依据指定的SocketAddress试图建立连接，假设本地地址没有设置，就会自己主动分配，等价于：

ClientBootstrap b = ....;

b.connect(remoteAddress, b.getOption("localAddress"));

静态方法 Channels.pipeline(ChannelHandler... handlers)用參数所指定的ChannelHandler 来创建一个新的ChannelPipeline，当然它们是有顺序的，我们也能够自己一个一个的加入。

 public static ChannelPipeline pipeline(ChannelHandler...
handlers) {

        if (handlers == null) {

            throw new NullPointerException( "handlers");

        }

        ChannelPipeline newPipeline = pipeline ();

        for (int i = 0; i < handlers. length;
i ++) {

            ChannelHandler h = handlers[i];

            if (h == null) {

                break;

            }

            newPipeline.addLast(ConversionUtil. toString(i), h);

        }

        return newPipeline;

    }

2. server端细节分析

服务器端构建的基本流程和client类似，仅仅是这里的ChannelFactory。Bootstrap 都要满足作为server的特性。

NioServerSocketChannelFactory创建server端的，基于NIO的ServerSocketChannel。仍然是非堵塞模式。

每一个绑定的ServerSocketChannel 有自身的boos thread，比方说打开监听了两个port 80,443。那么就会有两个boss thread，各自负责各自port的连接请求，直到那个port解绑定，然后将接受的连接请求交给worker
thread去处理。

这里是面向连接传输的ClientBootstrap 和  ServerBootstrap 。假设想用UDP的话就选 ConnectionlessBootstrap。

3. ChannelHandler的常见使用方法就会依据详细的事件类型做出详细的处理。牵扯到读写管道。并且有上下流的情况。

一个简单的netty样例：

TimeClientl.java

import java.net.InetSocketAddress;
import java.util.concurrent.Executors;

import org.jboss.netty.bootstrap.ClientBootstrap;
import org.jboss.netty.channel.ChannelFactory;
import org.jboss.netty.channel.ChannelPipeline;
import org.jboss.netty.channel.ChannelPipelineFactory;
import org.jboss.netty.channel.Channels;
import org.jboss.netty.channel.socket.nio.NioClientSocketChannelFactory;

public class TimeClient {
	public static void main(String[] args) {
		String host = args[0];
		int port = Integer.parseInt(args[1]);

		ChannelFactory factory = new NioClientSocketChannelFactory(
				Executors.newCachedThreadPool(), Executors.newCachedThreadPool());
		ClientBootstrap bootstrap = new ClientBootstrap(factory);
		bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
			@Override
			public ChannelPipeline getPipeline() throws Exception {
				return Channels.pipeline(new TimeClientHandler2());
			}
		});
		bootstrap.connect(new InetSocketAddress(host, port));  //
	}

}

TimeClientHandler.java

import java.util.Date;

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.ExceptionEvent;
import org.jboss.netty.channel.MessageEvent;
import org.jboss.netty.channel.SimpleChannelHandler;

public class TimeClientHandler extends SimpleChannelHandler{
	@Override
	public void messageReceived(ChannelHandlerContext ctx, MessageEvent e)
			throws Exception {
		ChannelBuffer buffer = (ChannelBuffer)e.getMessage();
		long currentTimeMills = buffer.readInt() * 1000L;
		System.out.println(new Date(currentTimeMills));
		e.getChannel().close();
	}

	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e)
			throws Exception {
		e.getCause().printStackTrace();
		Channel c = e.getChannel();
		c.close();
	}
}

TimeServer.java

import java.net.InetSocketAddress;
import java.util.concurrent.Executors;

import org.jboss.netty.bootstrap.ServerBootstrap;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelFactory;
import org.jboss.netty.channel.ChannelPipeline;
import org.jboss.netty.channel.ChannelPipelineFactory;
import org.jboss.netty.channel.Channels;
import org.jboss.netty.channel.group.ChannelGroup;
import org.jboss.netty.channel.group.ChannelGroupFuture;
import org.jboss.netty.channel.group.DefaultChannelGroup;
import org.jboss.netty.channel.socket.nio.NioServerSocketChannelFactory;

public class TimeServer {
	public static ChannelGroup allChannels = new DefaultChannelGroup("time-server");

	public static void main(String[] args) {
		ChannelFactory factory = new NioServerSocketChannelFactory(
				Executors.newCachedThreadPool(),
				Executors.newCachedThreadPool());

		ServerBootstrap bootstrap = new ServerBootstrap(factory);
		bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
			@Override
			public ChannelPipeline getPipeline() throws Exception {
				return Channels.pipeline(new TimeServerHandler2(),
										 new TimeEncoder());
			}
		});

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

		Channel channel = bootstrap.bind(new InetSocketAddress(8080));

		allChannels.add(channel);
		//waitForShutdownCommand();  this is a imaginary logic:for instance
		//when there is accepted connection we close this server ;
		if(allChannels.size() >=2){
			ChannelGroupFuture f = allChannels.close();
			f.awaitUninterruptibly();
			factory.releaseExternalResources();
		}
	}
}

TimeServerHandler.java

import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelFuture;
import org.jboss.netty.channel.ChannelFutureListener;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.ChannelStateEvent;
import org.jboss.netty.channel.ExceptionEvent;
import org.jboss.netty.channel.SimpleChannelHandler;

public class TimeServerHandler extends SimpleChannelHandler{
	@Override
	public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e)
			throws Exception {
		Channel ch = e.getChannel();
		ChannelBuffer time = ChannelBuffers.buffer(4); //sizeof int
		time.writeInt((int)(System.currentTimeMillis()/1000L + 2208988800L));

		ChannelFuture cf = ch.write(time);
		cf.addListener(new ChannelFutureListener() {
			@Override
			public void operationComplete(ChannelFuture future) throws Exception {
				Channel ch = future.getChannel();
				ch.close();
			}
		});
	}
	@Override
	public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e)
			throws Exception {
		e.getCause().printStackTrace();
		Channel c = e.getChannel();
		c.close();
	}
}