Netty是基於事件驅動的、非同步的網路應用程式框架和工具，用以快速開發高效能、高可靠性的網路伺服器和客戶端程式。是一種NIO框架，下面從最簡單的Hello World示例開始，演示服務端和客戶端互動進行Netty互動。

1.首先,建立服務端

public class DiscardServer {
	
	private int port;
	
	public DiscardServer(int port) {
		super();
		this.port = port;
	}
	
	public void run() {
		//配置Server
				ServerBootstrap bootstrap = new ServerBootstrap(new NioServerSocketChannelFactory(
						Executors.newCachedThreadPool(),
						Executors.newCachedThreadPool()
				));
				
				//設定pipeFactory
				bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
					
					@Override
					public ChannelPipeline getPipeline() throws Exception {
						ChannelPipeline pipeline = Channels.pipeline(new DiscardServerHandler());
						return pipeline;
					}
				});
				
				//繫結server端埠
				bootstrap.bind(new InetSocketAddress(port));
	}

	public static void main(String[] args) {
		new DiscardServer(8080).run();
	}


	public int getPort() {
		return port;
	}


	public void setPort(int port) {
		this.port = port;
	}
	
	
}
 

2、建立服務端事件處理的站點Handler,裡面包含回撥方法用於處理與客戶端互動時的操作。

class DiscardServerHandler extends SimpleChannelHandler {
	
	@Override
	public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e)
			throws Exception {
		System.out.println("--------服務端-------");
		String str = "Hello world, I'm server";
		ChannelBuffer buffer = ChannelBuffers.buffer(str.length());
		buffer.writeBytes(str.getBytes());
		e.getChannel().write(buffer);
	}
	
	@Override
	public void messageReceived(ChannelHandlerContext ctx, MessageEvent e)
			throws Exception {
		ChannelBuffer buffer = (ChannelBuffer) e.getMessage();
		System.out.println("服務端接收到訊息:" + buffer.toString(Charset.defaultCharset()));
	}
	
}
 

3、建立客戶端

public class TimeClient {
	
	 private String host;  
	 private int port; 
	
	public TimeClient(String host, int port) {
		super();
		this.host = host;
		this.port = port;
	}
	
	public void run() {
		ClientBootstrap bootstrap = new ClientBootstrap( 
				new NioClientSocketChannelFactory(
						Executors.newCachedThreadPool(),
						Executors.newCachedThreadPool()
				)
			);
			
			bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
				//ChannelPipeline 管道、傳輸途徑
				@Override
				public ChannelPipeline getPipeline() throws Exception {
//					ChannelPipeline pipeline = Channels.pipeline();
//					pipeline.addLast("encode", new StringEncoder());
//					pipeline.addLast("decode", new StringDecoder());
//					pipeline.addLast("handler", new TimeClientHandler());
					return Channels.pipeline(new TimeClientHandler());
				}
			});
			
//			bootstrap.setOption("tcpNoDelay", true);
//			bootstrap.setOption("keepAlive", true);
			 // Start the connection attempt.  
			ChannelFuture future = bootstrap.connect(new InetSocketAddress(host, port));  
			 
			// Wait until the connection is closed or the connection attempt fails.  
			future.getChannel().getCloseFuture().awaitUninterruptibly();  
		
			// Shut down thread pools to exit.  
			bootstrap.releaseExternalResources();  

	}


	public static void main(String[] args) {
		new TimeClient("127.0.0.1", 8080).run();
	}



	public String getHost() {
		return host;
	}



	public void setHost(String host) {
		this.host = host;
	}



	public int getPort() {
		return port;
	}



	public void setPort(int port) {
		this.port = port;
	}
	
	
	
}
 

4、建立客戶端的Handler

class TimeClientHandler extends SimpleChannelHandler {
	
	//這個屬於事件相關的處理
	@Override
	public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e)
			throws Exception {
		System.out.println("-----------客戶端---------------");
		String msg = "Hello world, I'm client";
		ChannelBuffer buffer = ChannelBuffers.buffer(msg.length());
		buffer.writeBytes(msg.getBytes());
		e.getChannel().write(buffer);
	}
	
	 @Override  
	 public void messageReceived(  
	     ChannelHandlerContext ctx, MessageEvent e) {  
	 // Send back the received message to the remote peer.  
	 ChannelBuffer acceptBuff = (ChannelBuffer) e.getMessage();  
	 String info = acceptBuff.toString(Charset.defaultCharset());  
	 System.out.println("客戶端接收到訊息:" + info);  
	 e.getChannel().close();  
	 }  

	
}

5、先啟動server端,再啟動client端。可以分別在服務端和客戶端的控制檯看到如下訊息:

server console:
--------服務端-------
服務端接收到訊息:Hello world, I'm client

client console:
-----------客戶端---------------
客戶端接收到訊息:Hello world, I'm server

6、注意在handler中,傳遞字串必須以ChannelBuffer為載體,不能直接用String傳遞。
   當客戶端和服務端連線上後,先回調的是channelConnected方法;之後才是messageReceived方法。
   至此,就完成了Netty客戶端與服務端的簡單互動!