Netty字符串类型消息粘包/半包问题解决方案一示例代码：DelimiterBasedFrameDecoder+StringDecoder

• 原理

使用特殊的字符，将其作为数据包的结束位置，使TCP能够区分完整的业务应用数据边界，按照边界完整地接受Netty传输的数据；
此特殊字符需要保证正式报文数据里面不会出现相同的字符，以免破坏消息传输的完整性

• 代码

1.DelimiterBaseServer：服务器

/**
 * 服务器
 * @author pdc
 */
public class DelimiterBaseServer {

    //字符串分隔符
    private static final String delimiter_tag = "@#";

    public static void main(String[] args) throws Exception {
        int port = 8080;
        new DelimiterBaseServer().bind(port);
    }

    public void bind(int port) throws Exception {
        //创建两个EventLoopGroup实例
        //EventLoopGroup是包含一组专门用于处理网络事件的NIO线程组
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            //创建服务端辅助启动类ServerBootstrap对象
            ServerBootstrap b = new ServerBootstrap();
            //设置NIO线程组
            b.group(bossGroup, workerGroup)
                    //设置NioServerSocketChannel,对应与JDK NIO类ServerSocketChannel类
                    .channel(NioServerSocketChannel.class)
                    //设置TCP参数,连接请求的最大队列长度
                    .option(ChannelOption.SO_BACKLOG, 1024)
                    //设置I/O事件处理类,用来处理消息的编解码以及我们的业务逻辑
                    .childHandler(new ChannelInitializer<NioSocketChannel>() {
                        @Override
                        protected void initChannel(NioSocketChannel ch) throws Exception {
                            //设置DelimiterBasedFrameDecoder处理器
                            ByteBuf delimiter = Unpooled.copiedBuffer(delimiter_tag.getBytes());
                            ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter));
                            //设置StringDecoder处理器
                            ch.pipeline().addLast(new StringDecoder());
                            ch.pipeline().addLast(new DelimiterBaseServerHandler());
                        }
                    });
            // 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();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 优雅退出释放线程池资源
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

2.DelimiterBaseServerHandler：服务端业务逻辑处理类

/**
 * @author pdc
 */
public class DelimiterBaseServerHandler extends SimpleChannelInboundHandler {

    //字符串分隔符
    private static final String delimiter_tag = "@#";
    //计数器
    private static final AtomicInteger counter = new AtomicInteger(0);

    @Override
    public void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
        //接收客户端发送的字符串,并打印到控制台
        String content = (String) msg;
        System.out.println("received from client:" + content + " counter:" + counter.addAndGet(1));
        //将数据重新发送到客户端
        content += delimiter_tag;
        ByteBuf echo = Unpooled.copiedBuffer(content.getBytes());
        ctx.writeAndFlush(echo);
    }

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

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

3.DelimiterBaseClient：客户端

/**
 * 客户端
 * @author pdc
 */
public class DelimiterBaseClient {

    //字符串分隔符
    private static final String delimiter_tag = "@#";

    public static void main(String[] args) throws Exception {
        int port = 8080;
        new DelimiterBaseClient().connect(port, "127.0.0.1");
    }

    public void connect(int port, String host) throws Exception {
        //创建客户端处理I/O读写的NIO线程组
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            //创建客户端辅助启动类
            Bootstrap b = new Bootstrap();
            //设置NIO线程组
            b.group(group)
                    //设置NioSocketChannel,对应与JDK NIO类SocketChannel类
                    .channel(NioSocketChannel.class)
                    //设置TCP参数TCP_NODELAY
                    .option(ChannelOption.TCP_NODELAY, true)
                    .handler(new ChannelInitializer<NioSocketChannel>() {
                        @Override
                        protected void initChannel(NioSocketChannel ch) throws Exception {
                            //设置DelimiterBasedFrameDecoder处理器
                            ByteBuf delimiter = Unpooled.copiedBuffer(delimiter_tag.getBytes());
                            ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024, delimiter));
                            //设置StringDecoder处理器
                            ch.pipeline().addLast(new StringDecoder());
                            //配置客户端处理网络I/O事件的类
                            ch.pipeline().addLast(new DelimiterBaseClientHandler());
                        }
                    });
            // 发起异步连接操作
            ChannelFuture f = b.connect(host, port).sync();
            //循环发送1000次
            for (int i = 0; i < 1000; i++) {
                //构造客户端发送的数据ByteBuf对象
                String content = "你好,Netty!" + delimiter_tag;
                byte[] req = content.getBytes();
                ByteBuf messageBuffer = Unpooled.buffer(req.length);
                messageBuffer.writeBytes(req);
                //向服务端发送数据
                ChannelFuture channelFuture = f.channel().writeAndFlush(messageBuffer);
                channelFuture.syncUninterruptibly();
            }
            // 等待客户端链路关闭
            f.channel().closeFuture().sync();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 优雅退出,释放NIO线程组
            group.shutdownGracefully();
        }
    }
}

4.DelimiterBaseClientHandler：客户端逻辑处理类

/**
 * @author pdc
 */
public class DelimiterBaseClientHandler extends SimpleChannelInboundHandler {

    private static final Logger logger = Logger.getLogger(DelimiterBaseClientHandler.class.getName());
    //计数器
    private static final AtomicInteger counter = new AtomicInteger(0);
    //服务端响应请求返回数据的时候会自动调用该方法,我们通过实现该方法来接收服务端返回的数据,并实现客户端调用的业务逻辑
    @Override
    public void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
        //获取服务端返回的数据,并打印到控制台
        String content = (String) msg;
        System.out.println("received from server:" + content + " counter:" + counter.addAndGet(1));
    }
    //发生异常,关闭链路
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        logger.warning("Unexpected exception from downstream :" + cause.getMessage());
        ctx.close();
    }
}

• 运行

先运行DelimiterBaseServer的main，再运行DelimiterBaseClient的main即可