三 Netty使用和常见组件

1 介绍

1.1 Netty优势

API使用简单，开发门槛低

功能强大，支持多种主流协议

定制能力强，通过channel Handler对通信框架进行灵活的拓展

性能高，通过与其它主流NIO框架相比，Netty性能最优

成熟、稳定

社区活跃，版本迭代周期短，发现的BUG可以被及时的修复

 1.2 Netty核心组件

Bootstrap：启动类和主入口类；客户端和服务端的

EventLoop：线程，将channel发生的事件做循环处理

EventLoopGroup：线程组

Channel：Socket/SocketChannel

事件：网络上发生的事包装成事件；入站事件/出站事件

ChannelHandler：处理事件（加密、压缩等）

ChannelPipeline：一个个 ChannelHandler 构成的链路；责任链模式/过滤器

ChannelFuture：获取异步执行的结果

 2 实战

2.1 服务端

public class Server {

    private final int port = 8080;

    public static void main(String[] args) throws InterruptedException {
        Server server = new Server();
        server.start();
    }

    public void start() throws InterruptedException {
        //线程组
        NioEventLoopGroup group = new NioEventLoopGroup();
        //服务端启动必备
        ServerBootstrap bootstrap = new ServerBootstrap();
        try {
            bootstrap.group(group)
                    .channel(NioServerSocketChannel.class)
                    .localAddress(new InetSocketAddress(port))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new ServerHandler());
                        }
                    });
            //异步绑定服务器，阻塞直到完成
            ChannelFuture future = bootstrap.bind().sync();
            future.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }

public class ServerHandler extends ChannelInboundHandlerAdapter {

    //读取客户端传的数据
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg/*传递的消息*/) throws Exception {
        ByteBuf in = (ByteBuf) msg;
        System.out.println("Server accept :" + in.toString(StandardCharsets.UTF_8));
        ctx.writeAndFlush(in);
        ctx.close();
    }

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

2.2 客户端

public class Client {

    private final int port = 8080;
    private final String host = "127.0.0.1";

    public static void main(String[] args) throws InterruptedException {
        new Client().start();
    }

    public void start() throws InterruptedException {
        //Group线程组
        NioEventLoopGroup group = new NioEventLoopGroup();
        //客户端启动类
        Bootstrap bootstrap = new Bootstrap();
        try {
            bootstrap.group(group)
                    .channel(NioSocketChannel.class)
                    //指定服务器的IP地址和端口，和服务器的不同
                    .remoteAddress(new InetSocketAddress(host, port))
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new ClientHandler());
                        }
                    });
            ChannelFuture future = bootstrap.connect().sync();
            future.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }
}

public class ClientHandler extends SimpleChannelInboundHandler<ByteBuf> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
        System.out.println("client Accept" + msg.toString(CharsetUtil.UTF_8));
        ctx.close();
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.writeAndFlush(Unpooled.copiedBuffer("Hello Netty", CharsetUtil.UTF_8));
    }
}