概述

Netty主要实现了对NIO（BIO也进行了封装，不过通常不用）的封装。
把NIO封装成AIO的样子。
Linux下AIO的效率未必比NIO高（底层都是基于epoll机制，AIO只是多了一层封装，转换成异步）。
windows的服务器比较少，netty不重点考虑，也就是说Netty主要用在Linux上。

环境搭建

        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.1.82.Final</version>
        </dependency>

入门示例

服务端代码

package com.study.nettystudy.netty;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
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 io.netty.util.CharsetUtil;

public class NettyServer {
    public static void main(String[] args) throws InterruptedException {
        EventLoopGroup boss = new NioEventLoopGroup();
        EventLoopGroup worker = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(boss, worker)
                    .channel(NioServerSocketChannel.class) // 使用NioServerSocketChannel去处理accept连接，类似于Nio中ServerSocketChannel.accept();
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            // 建立会话通道后的通道配置
                            ch.pipeline().addLast(new SimpleServerHandler());
                        }
                    });

            ChannelFuture future = b.bind(8888).sync();
            future.channel().closeFuture().sync();
        } finally {
            worker.shutdownGracefully();
            boss.shutdownGracefully();
        }
    }
}

class SimpleServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        ByteBuf buffer = (ByteBuf) msg;
        System.out.println(buffer.toString(CharsetUtil.UTF_8));
        ctx.writeAndFlush(msg);
        ctx.close();
    }

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

客户端代码

客户端可以使用之前的客户的端，也可以使用Netty写一个客户端，代码如下：

package com.study.nettystudy.netty;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.util.ReferenceCountUtil;

public class NettyClient {
    public static void main(String[] args) {
        NioEventLoopGroup worker = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(worker);
            b.channel(NioSocketChannel.class);
            b.option(ChannelOption.SO_KEEPALIVE, true);
            b.handler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new TimeClientHandler());
                }
            });

            ChannelFuture f = b.connect("127.0.0.1", 8888).sync();
            // Wait until the connection is closed.
            f.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            worker.shutdownGracefully();
        }
    }
}

class TimeClientHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        final ChannelFuture future = ctx.writeAndFlush(Unpooled.copiedBuffer("hello netty server".getBytes()));
        future.addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture channelFuture) throws Exception {
                System.out.println("msg send");
            }
        });
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        try {
            ByteBuf m = (ByteBuf) msg;
            System.out.println(m.toString());
            ctx.close();
        } finally {
            ReferenceCountUtil.release(msg);
        }
    }

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