2.未处理示例

public class TimeClientHandler extends ChannelHandlerAdapter {

    private static final Logger logger = Logger
            .getLogger(TimeClientHandler.class.getName());

    private int counter;

    private byte[] req;

    /**
     * Creates a client-side handler.
     */
    public TimeClientHandler() {
        req = ("QUERY TIME ORDER" + System.getProperty("line.separator"))
                .getBytes();
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        ByteBuf message = null;
        for (int i = 0; i < 10; i++) {
            message = Unpooled.buffer(req.length);
            message.writeBytes(req);
            ctx.writeAndFlush(message);
        }
    }

    @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 + " ; the counter is : "
                + ++counter);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        // 释放资源
        logger.warning("Unexpected exception from downstream : "
                + cause.getMessage());
        ctx.close();
    }
}

public class TimeServerHandler extends ChannelHandlerAdapter {

    private int counter;

    @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").substring(0, req.length
                - System.getProperty("line.separator").length());
        System.out.println("The time server receive order : " + body
                + " ; the counter is : " + ++counter);
        String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new java.util.Date(
                System.currentTimeMillis()).toString() : "BAD ORDER";
        currentTime = currentTime + System.getProperty("line.separator");
        ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes());
        ctx.writeAndFlush(resp);
    }

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

输出结果,发生了粘包，10个数据包在一起接收到

The time server receive order : QUERY TIME ORDER
QUERY TIME ORDER
QUERY TIME ORDER
QUERY TIME ORDER
QUERY TIME ORDER
QUERY TIME ORDER
QUERY TIME ORDER
QUERY TIME ORDER
QUERY TIME ORDER
QUERY TIME ORDER ; the counter is : 1

3.使用LineBasedFrameDecoder解决粘包问题

基于行来进行消息粘包拆包处理,使用了行尾控制字符（\n 或者\r\n）来解析消息数据

    private class ChildChannelHandler extends ChannelInitializer<SocketChannel> {
        @Override
        protected void initChannel(SocketChannel arg0) throws Exception {
            arg0.pipeline().addLast(new LineBasedFrameDecoder(1024));
            arg0.pipeline().addLast(new StringDecoder());
            arg0.pipeline().addLast(new TimeServerHandler());
        }
}

输出结果:

The time server receive order : QUERY TIME ORDER ; the counter is : 1
The time server receive order : QUERY TIME ORDER ; the counter is : 2
The time server receive order : QUERY TIME ORDER ; the counter is : 3
The time server receive order : QUERY TIME ORDER ; the counter is : 4
The time server receive order : QUERY TIME ORDER ; the counter is : 5
The time server receive order : QUERY TIME ORDER ; the counter is : 6
The time server receive order : QUERY TIME ORDER ; the counter is : 7
The time server receive order : QUERY TIME ORDER ; the counter is : 8
The time server receive order : QUERY TIME ORDER ; the counter is : 9
The time server receive order : QUERY TIME ORDER ; the counter is : 10

4.DelimiterBasedFrameDecoder

以分隔符作为码流结束标识的消息的解码

下面示例:
DelimiterBasedFrameDecoder的分隔符为$_

static final String ECHO_REQ = "Hi, Lilinfeng. Welcome to Netty.$_";

   public void connect(int port, String host) throws Exception {
        // 配置客户端NIO线程组
        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 {
                            ByteBuf delimiter = Unpooled.copiedBuffer("$_"
                                    .getBytes());
                            ch.pipeline().addLast(
                                    new DelimiterBasedFrameDecoder(1024,
                                            delimiter));
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new EchoClientHandler());
                        }
                    });

            // 发起异步连接操作
            ChannelFuture f = b.connect(host, port).sync();

            // 当代客户端链路关闭
            f.channel().closeFuture().sync();
        } finally {
            // 优雅退出，释放NIO线程组
            group.shutdownGracefully();
        }
    }

输出消息结果:

This is 1 times receive client : [Hi, Lilinfeng. Welcome to Netty.]
This is 2 times receive client : [Hi, Lilinfeng. Welcome to Netty.]
This is 3 times receive client : [Hi, Lilinfeng. Welcome to Netty.]
This is 4 times receive client : [Hi, Lilinfeng. Welcome to Netty.]
This is 5 times receive client : [Hi, Lilinfeng. Welcome to Netty.]
This is 6 times receive client : [Hi, Lilinfeng. Welcome to Netty.]
This is 7 times receive client : [Hi, Lilinfeng. Welcome to Netty.]
This is 8 times receive client : [Hi, Lilinfeng. Welcome to Netty.]
This is 9 times receive client : [Hi, Lilinfeng. Welcome to Netty.]
This is 10 times receive client : [Hi, Lilinfeng. Welcome to Netty.]

5.FixedLengthFrameDecoder

固定长度解码
new FixedLengthFrameDecoder(20)表示固定长度20解码

    public void bind(int port) throws Exception {
        // 配置服务端的NIO线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 100)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch)
                                throws Exception {
                            ch.pipeline().addLast(
                                    new FixedLengthFrameDecoder(20));
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new EchoServerHandler());
                        }
                    });

            // 绑定端口，同步等待成功
            ChannelFuture f = b.bind(port).sync();

            // 等待服务端监听端口关闭
            f.channel().closeFuture().sync();
        } finally {
            // 优雅退出，释放线程池资源
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

输出消息结果:为固定长度20

Receive client : [Hi, Lilinfeng. Welco]
Receive client : [me to Netty.$_Hi, Li]
Receive client : [linfeng. Welcome to ]
Receive client : [Netty.$_Hi, Lilinfen]
Receive client : [g. Welcome to Netty.]
Receive client : [$_Hi, Lilinfeng. Wel]
Receive client : [come to Netty.$_Hi, ]
Receive client : [Lilinfeng. Welcome t]
Receive client : [o Netty.$_Hi, Lilinf]

6.LengthFieldBasedFrameDecoder

自定义包协议,如果需要自定义协议，可以使用此解码器

https://www.jishux.com/p/00ad4d5d4d4ed50d

参考:
https://my.oschina.net/andylucc/blog/625315
https://blog.csdn.net/scythe666/article/details/51996268