Netty框架学习之路（二）—— 一个简单的Netty程序

前言

上一篇博文中主要介绍了三种IO模式，Netty是一个高性能、异步事件驱动的Java NIO框架，本文以一个简单的Netty程序带领大家先来领略一下Netty的风采，程序的功能主要是获取当前的服务器时间。

客户端

TimeClient.java

public class TimeClient {

    public void connect(int port, String host) throws Exception{
        EventLoopGroup group = new NioEventLoopGroup();

        try {
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception{
                            ch.pipeline().addLast(new TimeClientHandler());
                        }
                    });

            ChannelFuture f = b.connect(host, port).sync();

            f.channel().closeFuture().sync();
        }finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception{
        int port = 8800;
        new TimeClient().connect(port, "localhost");
    }
}

TimeClientHandler.java

public class TimeClientHandler extends ChannelHandlerAdapter {

    private final ByteBuf firstMessage;

    public TimeClientHandler(){
        byte[] req = "QUERY TIME ORDER".getBytes();
        firstMessage = Unpooled.buffer(req.length);
        firstMessage.writeBytes(req);
    }

    public void channelActive(ChannelHandlerContext ctx){
        ctx.writeAndFlush(firstMessage);
    }
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception{
        ByteBuf buf = (ByteBuf)msg;
        byte[] req = new byte[buf.readableBytes()];
        buf.readBytes(req);

        String body = new String(req, "UTF-8");

        System.out.println("Now is : " + body);
    }

    public void exceptionCaught(ChannelHandlerContext ctx) throws Exception{
        ctx.close();
    }
}

服务端

TimeServer.java

public class TimeServer {
    public void bind(int port) throws Exception{
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    .childHandler(new ChannelInitializer<SocketChannel>(){
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new TimeServerHandler());
                        }
                    });

            ChannelFuture f = b.bind(port).sync();

            f.channel().closeFuture().sync();

        }finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception{
        int port = 8800;
        new TimeServer().bind(port);
    }
}

TimeServerHandler.java

public class TimeServerHandler extends ChannelHandlerAdapter {

    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception{
        ByteBuf buf = (ByteBuf)msg;
        byte[] req = new byte[buf.readableBytes()];
        buf.readBytes(req);

        String body = new String(req, "UTF-8");

        System.out.println("The time server receive order : " + body);

        String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body)?new Date(System.currentTimeMillis()).toString() : "BAD ORDER";
        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.write(resp);
    }

    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception{
        ctx.flush();
    }

    public void exceptionCaught(ChannelHandlerContext ctx) throws Exception{
        ctx.close();
    }
}

运行结果

客户端

服务端

总结

“蚊子虽小，五脏俱全”。上述代码功能虽然简单，但是却涵盖了例如Channel、ChannelPipeline、EventLoopGroup、EventLoopGroup等Netty最核心的组件，这些核心组件会在后续的博文中详细讲述。