Java NIO(五)Netty框架简单应用

Netty是一款基于NIO开发的网络通信框架，Netty能通过编程自定义各种协议，因为netty能够通过自己来编码/解码字节流。本文只是对netty的简单应用。。

关于Netty的一本书“Netty权威指南”，中提到了为什么要选择Netty。

下面对上一篇文章中的Server/Client（客户端向服务器端发送“query”字符串，服务器端响应给客户端一个当前系统时间）改造成用Netty框架实现。

//Server的实现
public class NettyServer {

    public void bind(int port) throws Exception{

        //配置服务端的NIO线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG,1024)
                    .childHandler(new NettyServerInit());//最后一步的NettyServerInit需要自己实现
            //绑定端口同步等待成功。
            Channel ch = b.bind("localhost",port).sync().channel();
            ch.closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        new NettyServer().bind(55556);
    }
}

NettyServerInit的实现：

public class NettyServerInit extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel socketChannel) throws Exception {
        socketChannel.pipeline().addLast(new NettyServerHandler());
    }
}

NettyServerHandler的实现：

public class NettyServerHandler extends ChannelHandlerAdapter {

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws UnsupportedEncodingException {
        ByteBuf buf = (ByteBuf) msg;
        byte[] req = new byte[buf.readableBytes()];
        buf.readBytes(req);
        String body = new String(req,"UTF-8");
        System.out.println("收到客户端消息:" + body);
        String currentTime = "query".equalsIgnoreCase(body)?new java.util.Date(System.currentTimeMillis()).toString():"error";

        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.write(resp);
    }

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

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

客户端的实现：

//Client的实现
public class NettyClient {

    public void connect(int port,String host) throws InterruptedException {
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group).channel(NioSocketChannel.class)
                    .option(ChannelOption.TCP_NODELAY,true)
                    .handler(new ChannelInitializer<NioSocketChannel>() {
                        @Override
                        protected void initChannel(NioSocketChannel nioSocketChannel) throws Exception {
                            nioSocketChannel.pipeline().addLast(new NettyClientHandler());
                        }
                    });
            //发起连接操作
            ChannelFuture f = b.connect(host,port).sync();
            f.channel().closeFuture().sync();
        }finally {
            group.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new NettyClient().connect(55556,"localhost");
    }
}

NettyClientHandler的实现：

public class NettyClientHandler extends ChannelHandlerAdapter {

    private final ByteBuf firstMessage;

    public NettyClientHandler() {
        byte[] req = "query".getBytes();
        firstMessage = Unpooled.buffer(req.length);
        firstMessage.writeBytes(req);
    }

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

    @Override
    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);
    }

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

通过上面的代码可以发现，实现同样的功能，利用Netty去实现，代码量会减少很多，业务逻辑也相对简单。