1. 目标

基于Netty实现Server端，并成功启动Server端，监听端口 $\color{green}{8081}$ ，并打印接收到的消息
利用telnet连接1中启动成功的Server端，并发送消息 $\color{#0099ff}{Hello Server}$

2. 准备工作

IntelliJ IDEA + Maven + Netty 4.1.36.Final版本

首先通过IDEA新建一个Maven项目，并引入所要依赖Netty的版本
这里选择目前最新的版本 $\color{red}{4.1.36.Final}$

<!-- https://mvnrepository.com/artifact/io.netty/netty-all -->
    <dependency>
        <groupId>io.netty</groupId>
        <artifactId>netty-all</artifactId>
        <version>4.1.36.Final</version>
    </dependency>

01.png

其中handler包用于编写所有Server端所需的Handler，Server类则作为整个Server的启动类

3. 编码

handler包下新建ServerInboundHandler类

该类继承Netty提供的入站处理器ChannelInboundHandlerAdapter

public class ServerInboundHandler extends ChannelInboundHandlerAdapter {

@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
    super.channelActive(ctx);
}

@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
    // 1.
    ByteBuf in = (ByteBuf) msg;
    StringBuilder sMsg = new StringBuilder();
    while (in.isReadable()) {
        sMsg.append((char) in.readByte());
    }
    System.out.println(sMsg.toString());
    super.channelRead(ctx, msg);
}

@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
    super.channelReadComplete(ctx);
}

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

编写Server类

public class Server {

// 监听端口
private int port;
private Server(int port) {
    this.port = port;
}

// 启动一个Server服务器
private void start() throws InterruptedException {
    // 1.
    EventLoopGroup bossGroup = new NioEventLoopGroup(1);
    EventLoopGroup workerGroup = new NioEventLoopGroup();
    try {
        // 2.
        ServerBootstrap serverBootstrap = new ServerBootstrap();
        serverBootstrap.group(bossGroup, workerGroup)
                // 3.
                .channel(NioServerSocketChannel.class)
                // 4.
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel ch) {
                        ch.pipeline().addLast(new ServerInboundHandler());
                    }
                })
                // 5.
                .option(ChannelOption.SO_BACKLOG, 128)
                // 6.
                .childOption(ChannelOption.SO_KEEPALIVE, true);

        System.out.println("Server is started");
        // 7.
        ChannelFuture f = serverBootstrap.bind(port).sync();

        // 8.
        f.channel().closeFuture().sync();
    }finally {
        // 9.
        workerGroup.shutdownGracefully();
        bossGroup.shutdownGracefully();
    }

}

public static void main(String[] args) throws InterruptedException {

    // 利用vm参数传递端口号，不传则默认8081
    int port;
    if (args.length > 0) {
        port = Integer.parseInt(args[0]);
    }else{
        port = 8081;
    }

    // 启动server
    System.out.println("Server to starting... the port is: " + port);
    new Server(port).start();
}
}