Netty入门教程

Netty 介绍

随着Java NIO的普及，越来越多基于nio的框架应运而生，netty便是其中之一，netty提供更快更容易的方式去操作实现各个通信协议，包括http tcp udpftp，smtp等等。

Netty 是一个高效的提供异步事件驱动的网络通信框架，换而言之，netty是一个nio实现框架并且能简化传统的tcp udp socket 编程。

Netty 编程

1.处理类

Client处理类

继承SimpleChannelInboundHandler类并重写相应方法如channelActive，channelRead和exceptionCaught

 

 

 

 

 

​

public class DiscardClientHandler extends SimpleChannelInboundHandler<Object> {

​

    private ByteBuf content;

    private ChannelHandlerContext ctx;

​

    @Override

    public void channelActive(ChannelHandlerContext ctx) {

        this.ctx = ctx;

​

        // Initialize the message.

        content = ctx.alloc().directBuffer(DiscardClient.SIZE).writeZero(DiscardClient.SIZE);

​

        // Send the initial messages.

        generateTraffic();

    }

​

    @Override

    public void channelInactive(ChannelHandlerContext ctx) {

        content.release();

    }

​

    @Override

    public void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {

        // Server is supposed to send nothing, but if it sends something, discard it.

    }

​

    @Override

    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {

        // Close the connection when an exception is raised.

        cause.printStackTrace();

        ctx.close();

    }

​

    long counter;

​

    private void generateTraffic() {

        // Flush the outbound buffer to the socket.

        // Once flushed, generate the same amount of traffic again.

        ctx.writeAndFlush(content.retainedDuplicate()).addListener(trafficGenerator);

    } c

​

    private final ChannelFutureListener trafficGenerator = new ChannelFutureListener() {

        @Override

        public void operationComplete(ChannelFuture future) {

            if (future.isSuccess()) {

                generateTraffic();

            } else {

                future.cause().printStackTrace();

                future.channel().close();

            }

        }

    };

}

 

Server处理类

同样继承SimpleChannelInboundHandler 并重写channelRead0和exceptionCaught方法

 

 

 

 

 

public class DiscardServerHandler extends SimpleChannelInboundHandler<Object> {

​

    @Override

    public void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {

        // discard

    }

​

    @Override

    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {

        // Close the connection when an exception is raised.

        cause.printStackTrace();

        ctx.close();

    }

}

 

​

2.连接类

Client连接

客户端连接需要用到Bootstrap和EventLoopGroup类，并借助ChannelInitializer将对应的处理器绑定

 

 

 

 

 

        EventLoopGroup group = new NioEventLoopGroup();

        try {

            Bootstrap b = new Bootstrap();

            b.group(group)

             .channel(NioSocketChannel.class)

             .handler(new ChannelInitializer<SocketChannel>() {

                 @Override

                 protected void initChannel(SocketChannel ch) throws Exception {

                     ChannelPipeline p = ch.pipeline();

                     if (sslCtx != null) {

                         p.addLast(sslCtx.newHandler(ch.alloc(), HOST, PORT));

                     }

                     p.addLast(new DiscardClientHandler());

                 }

             });

​

            // Make the connection attempt.

            ChannelFuture f = b.connect(HOST, PORT).sync();

​

            // Wait until the connection is closed.

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

        } finally {

            group.shutdownGracefully();

        }

 

Server连接

server连接需要两个EventLoopGroupon进行，boss负责接收请求，worker进行相应处理 ，并且使用ServerBootstrap进行连接。

 

 

 

 

 

        EventLoopGroup bossGroup = new NioEventLoopGroup(1);

        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {

            ServerBootstrap b = new ServerBootstrap();

            b.group(bossGroup, workerGroup)

             .channel(NioServerSocketChannel.class)

             .handler(new LoggingHandler(LogLevel.INFO))

             .childHandler(new ChannelInitializer<SocketChannel>() {

                 @Override

                 public void initChannel(SocketChannel ch) {

                     ChannelPipeline p = ch.pipeline();

                     if (sslCtx != null) {

                         p.addLast(sslCtx.newHandler(ch.alloc()));

                     }

                     p.addLast(new DiscardServerHandler());

                 }

             });

​

            // Bind and start to accept incoming connections.

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

​

            // Wait until the server socket is closed.

            // In this example, this does not happen, but you can do that to gracefully

            // shut down your server.

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

        } finally {

            workerGroup.shutdownGracefully();

            bossGroup.shutdownGracefully();

        }

 

以上就是一个简单的netty实例：

3.重要类分析：

io.netty.buffer. ByteBuf

 

 

 

 

 

public abstract class ByteBuf extends Object implements ReferenceCounted, Comparable<ByteBuf>

 

ByteBuf 提供了两个指针来进行顺序的读和写。- readerIndex 读操作 and writerIndex 写操作.

​ +-----------------------------------+--------------------------------------+------------------------------------------------+​ | discardable bytes | readable bytes | writable bytes |​ | | (CONTENT) | |​ +-----------------------------------+---------------------------------------+-----------------------------------------------+​ | | | |​ 0 <= readerIndex <= writerIndex <= capacity