133810279300203794.jpg

netty简单入门：
netty版本大致版本分为 netty3.x 和 netty4.x、netty5.x

netty可以运用在那些领域？

1分布式进程通信
例如: hadoop、dubbo、akka等具有分布式功能的框架，底层RPC通信都是基于netty实现的，这些框架使用的版本通常都还在用netty3.x

2、游戏服务器开发
最新的游戏服务器有部分公司可能已经开始采用netty4.x 或 netty5.x
1、netty服务端hello world案例
创建一个maven项目使用的pom依赖是

 <!-- https://mvnrepository.com/artifact/io.netty/netty-all -->
        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.1.21.Final</version>
        </dependency>

SimpleChannelHandler 处理消息接收和写
    - messageReceived接收消息
    - channelConnected新连接，通常用来检测IP是否是黑名单
    - channelDisconnected链接关闭，可以再用户断线的时候清楚用户的缓存数据等

2、netty客户端hello world案例

channelDisconnected与channelClosed的区别？
channelDisconnected只有在连接建立后断开才会调用 channelClosed无论连接是否成功都会调用关闭资源

下面看使用netty实现服务器端Server和客户端Client小栗子：
Server:

public class Server {
    public static void main(String[] args) {
        //创建一个服务类
        ServerBootstrap serverBootstrap = new ServerBootstrap();

        //创建2个线程池分别负责监听端口和处理通道读写任务
        ExecutorService boss = Executors.newCachedThreadPool();
        ExecutorService work = Executors.newCachedThreadPool();

        //设置Nio工厂
        serverBootstrap.setFactory(new NioServerSocketChannelFactory(boss,work));


        //设置管道工厂
        serverBootstrap.setPipelineFactory(new ChannelPipelineFactory() {
            @Override
            public ChannelPipeline getPipeline() throws Exception {
                ChannelPipeline pipeline = Channels.pipeline();
                pipeline.addLast("decoder",new StringDecoder());
                pipeline.addLast("encoder",new StringEncoder());
                pipeline.addLast("hellhandler",new HelloHandler());
                return pipeline;
            }
        });

        serverBootstrap.bind(new InetSocketAddress(10010));
        System.out.println("服务器启动...");

    }
}

Client:

public class Client {
    public static void main(String[] args) {
        //客户端服务类
        ClientBootstrap bootstrap = new ClientBootstrap();

        ExecutorService boss = Executors.newCachedThreadPool();
        ExecutorService work = Executors.newCachedThreadPool();

        bootstrap.setFactory(new NioClientSocketChannelFactory(boss,work));
        bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
            @Override
            public ChannelPipeline getPipeline() throws Exception {
                ChannelPipeline pipeline = Channels.pipeline();
                pipeline.addLast("decoder",new org.jboss.netty.handler.codec.string.StringDecoder());
                pipeline.addLast("encoder",new org.jboss.netty.handler.codec.string.StringEncoder());
                pipeline.addLast("hihandler",new HiHandler());
                return pipeline;
            }
        });

        ChannelFuture channelFuture = bootstrap.connect(new InetSocketAddress("192.168.213.1",10010));
        System.out.println("Client start...");
        Channel channel = channelFuture.getChannel();
        Scanner scanner = new Scanner(System.in);
        while(true){
            System.out.println("请输入");
            if(channel.isWritable()) {
                channel.write(scanner.next());
            }
        }
    }
}

HelloHandler和HiHandler代码一样:

public class HelloHandler extends SimpleChannelHandler {

    /**
     * 接受消息
     * @param ctx
     * @param e
     * @throws Exception
     */
    @Override
    public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
        String s = (String)e.getMessage();
        System.out.println(s);
       //回写数据
        if(ctx.getChannel().isWritable()) {
            ctx.getChannel().write("hi");
            super.messageReceived(ctx, e);
        }
    }

    /**
     * 捕获异常
     * @param ctx
     * @param e
     * @throws Exception
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) throws Exception {
        System.out.println("exceptionCaught");
        ctx.getChannel().close();
        System.out.println("连接关闭");
        //super.exceptionCaught(ctx, e);
    }

    /**
     * 新的连接进来
     * @param ctx
     * @param e
     * @throws Exception
     */
    @Override
    public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
        System.out.println("channelConnected");
        super.channelConnected(ctx, e);
    }

    /**
     * 连接已经建立后，通道断开连接
     * @param ctx
     * @param e
     * @throws Exception
     */
    @Override
    public void channelDisconnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
        System.out.println("channelDisconnected");
        super.channelDisconnected(ctx, e);
    }

    /**
     * 连接断开(包含了连接不上的情况)
     * @param ctx
     * @param e
     * @throws Exception
     */
    @Override
    public void channelClosed(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
        System.out.println("channelClosed");
        super.channelClosed(ctx, e);
    }
}

运行便可实现一个简单的聊天室的功能。
代码地址:项目git地址