Netty实战

一、Netty异步和事件驱动
1.Java网络编程回顾
socket.accept 阻塞
socket.setsockopt /非阻塞
2.NIO异步非阻塞
a).nio 非阻塞的关键时使用选择器(java.nio.channels.Selector)来实现；可以监控多个socket读写的完成状态来协调其他socket的读写，以提高资源使用率；
b).异步事件驱动，socket请求发起，立即响应，后端执行处理请求，处理完毕通知客户端；
c).Channel 链接实体的连接，请求和响应的载体；Netty通过回调来处理事件，时间触发->ChannelHandler->channelActive()来处理事件；
d).ChannelFuture通过ChannelFutureListener来监听事件提供通知处理完成的结果；Future是需要手动去获取结果；每个I/O操作都会立即返回一个ChannelFuture，不会阻塞，后台处理I/O,至于何时处理完成，异步时间驱动通知；
3.Nttey的异步变成模型建立在Future和回调的基础之上，再将时间派发到ChannelHandler之上进行处理；

二、Netty Demo
1.EchoServerHandler

package chap01;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.CharsetUtil;

@ChannelHandler.Sharable
public class EchoServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx,Object msg){
        ByteBuf in = (ByteBuf) msg;
        System.out.println("Server received: "+ in.toString(CharsetUtil.UTF_8));
        ctx.write(in);
    }
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx){
        ctx.writeAndFlush(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
    }
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx,Throwable cause){
        cause.printStackTrace();
        ctx.close();
    }
}

2.EchoServer

package chap01;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;

import java.net.InetSocketAddress;

public class EchoServer {
    private final int port;

    public  EchoServer(int port){
        this.port = port;
    }

    public static void main(String[] args) throws  Exception{
//        if (args.length !=-1){
//            System.err.println("Usage: " + EchoServer.class.getSimpleName()+"<port>");
//        }
//        int port = Integer.parseInt(args[0]);
//        new EchoServer(port).start();
        new EchoServer(9001).start();
    }

    public void start() throws Exception{
        final  EchoServerHandler serverHandler = new EchoServerHandler();
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(group).channel(NioServerSocketChannel.class).localAddress(new InetSocketAddress(port)).childHandler(new ChannelInitializer<SocketChannel>(){
               @Override
               public void initChannel(SocketChannel ch) throws Exception{
                   ch.pipeline().addLast(serverHandler);
               }
            });
            ChannelFuture f = b.bind().sync();
            f.channel().closeFuture().sync();
        }finally {
            group.shutdownGracefully().sync();
        }
    }
}

3.EchoClientHandler

package chap01;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.util.CharsetUtil;

public class EchoClientHandler extends SimpleChannelInboundHandler<ByteBuf> {
    @Override
    public void channelActive(ChannelHandlerContext ctx){
        ctx.writeAndFlush(Unpooled.copiedBuffer("Netty rocks!", CharsetUtil.UTF_8));
    }

    @Override
    public void channelRead0(ChannelHandlerContext ctx,ByteBuf in){
        System.out.println("Client received: "+in.toString(CharsetUtil.UTF_8));
    }

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

}

4.EchoClient

package chap01;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

import java.net.InetSocketAddress;

public class EchoClient {
    private final String host;
    private final int port;

    public EchoClient(String host,int port){
        this.host = host;
        this.port = port;
    }

    public void start() throws Exception{
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class).remoteAddress(new InetSocketAddress(host,port)).handler(new ChannelInitializer<SocketChannel>(){
               @Override
               public void initChannel(SocketChannel ch) throws Exception{
                   ch.pipeline().addLast(new EchoClientHandler());
               }
            });
            ChannelFuture f = b.connect().sync();
        }finally {
            group.shutdownGracefully().sync();
        }
    }

    public static void main(String[] args) throws  Exception{
//        if (args.length!=2){
//            System.err.println("Usage: "+EchoClient.class.getSimpleName() + "<host><port>");
//                    return;
//        }
//        String host = args[0];
//        int port = Integer.parseInt(args[1]);
//        new EchoClient(host,port).start();
        new EchoClient("127.0.0.1",9001).start();
    }
}

三、Netty组件和设计
1.Channel、Event Loop和ChannelFuture
a).Channel 即Socket，提供基本的I/O操作，bind(),connet(),read(),write()；Event Loop控制流的管理，和并发,Channel生命周期只和一个Event Loop进行绑定，多个EventLoop组成一个Event LoopGroup；Channel Future用以接收回调，Netty中所有的处理都是异步的，每个请求可能不会立即返回，addListener()方法会添加一个监听器ChannelFutureListener用来回调通知；
2.ChannelHandler、ChannelPipeLine
a).ChannelHandler 用于接受入站事件和数据；常用ChannelInBoundHandler；
b).ChannelPipeLine 提供了Channel Handler链的容器，一个Channel被创建时，她会被ChannelHandler安装到ChannelPipeLine中；