Netty（四）：粘包问题描述及解决

拆包粘包问题解决

netty使用tcp/ip协议传输数据。而tcp/ip协议是类似水流一样的数据传输方式。多次访问的时候有可能出现数据粘包的问题，解决这种问题的方式如下：

1 定长数据流

客户端和服务器，提前协调好，每个消息长度固定。（如：长度10）。如果客户端或服务器写出的数据不足10，则使用空白字符补足（如：使用空格）。

代码示例

a.客户端

public class MyClient {
    
    // 处理请求和处理服务端响应的线程组
    private EventLoopGroup group = null;
    // 服务启动相关配置信息
    private Bootstrap bootstrap = null;
    
    public MyClient(){
        init();
    }
    
    private void init(){
        group = new NioEventLoopGroup();
        bootstrap = new Bootstrap();
        // 绑定线程组
        bootstrap.group(group);
        // 设定通讯模式为NIO
        bootstrap.channel(NioSocketChannel.class);
    }
    
    public ChannelFuture doRequest(String host, int port) throws InterruptedException{
        this.bootstrap.handler(new ChannelInitializer<SocketChannel>() {

            @Override
            protected void initChannel(SocketChannel ch) throws Exception {
                ChannelHandler[] handlers = new ChannelHandler[3];
                handlers[0] = new FixedLengthFrameDecoder(3);
                // 字符串解码器Handler，会自动处理channelRead方法的msg参数，将ByteBuf类型的数据转换为字符串对象
                handlers[1] = new StringDecoder(Charset.forName("utf8"));
                handlers[2] = new MyClientHandler();
                
                ch.pipeline().addLast(handlers);
            }
        });
        ChannelFuture future = this.bootstrap.connect(host, port).sync();
        return future;
    }
    
    public void release(){
        this.group.shutdownGracefully();
    }
    
    public static void main(String[] args) {
        MyClient client = null;
        ChannelFuture future = null;
        try{
            client = new MyClient();
            
            future = client.doRequest("localhost", 8000);
            
            Scanner s = null;
            while(true){
                s = new Scanner(System.in);
                System.out.print("客户端输入：");
                future.channel().writeAndFlush(Unpooled.copiedBuffer(s.nextLine().getBytes("utf8")));
                TimeUnit.SECONDS.sleep(1);
            }
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            if(null != future){
                try {
                    future.channel().closeFuture().sync();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            if(null != client){
                client.release();
            }
        }
    }
    
}

public class MyClientHandler extends ChannelHandlerAdapter {

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        try{
            System.out.println("from server : " + msg.toString());
        }finally{
            // 用于释放缓存。避免内存溢出
            ReferenceCountUtil.release(msg);
        }
    }

    /**
     * 异常处理
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println(cause.getMessage());
        ctx.close();
    }

}

b.服务端

public class MyServer {
    private EventLoopGroup acceptorGroup = null;
    private EventLoopGroup clientGroup = null;
    private ServerBootstrap bootstrap = null;
    public MyServer(){
        init();
    }
    private void init(){
        acceptorGroup = new NioEventLoopGroup();
        clientGroup = new NioEventLoopGroup();
        bootstrap = new ServerBootstrap();
        // 绑定线程组
        bootstrap.group(acceptorGroup, clientGroup);
        // 设定通讯模式为NIO
        bootstrap.channel(NioServerSocketChannel.class);
        // 设定缓冲区大小
        bootstrap.option(ChannelOption.SO_BACKLOG, 1024);
        // SO_SNDBUF发送缓冲区，SO_RCVBUF接收缓冲区，SO_KEEPALIVE开启心跳监测（保证连接有效）
        bootstrap.option(ChannelOption.SO_SNDBUF, 8*1024)
            .option(ChannelOption.SO_RCVBUF, 8*1024)
            .option(ChannelOption.SO_KEEPALIVE, true);
    }
    public ChannelFuture doAccept(int port) throws InterruptedException{
        
        bootstrap.childHandler(new ChannelInitializer<SocketChannel>() {

            @Override
            protected void initChannel(SocketChannel ch) throws Exception {
                ChannelHandler[] acceptorHandlers = new ChannelHandler[3];
                // 定长Handler。通过构造参数设置消息长度（单位是字节）。发送的消息长度不足可以使用空格补全。
                acceptorHandlers[0] = new FixedLengthFrameDecoder(3);
                acceptorHandlers[1] = new StringDecoder(Charset.forName("utf8"));
                acceptorHandlers[2] = new MyServerHandler();
                ch.pipeline().addLast(acceptorHandlers);
            }
        });
        ChannelFuture future = bootstrap.bind(port).sync();
        return future;
    }
    public void release(){
        this.acceptorGroup.shutdownGracefully();
        this.clientGroup.shutdownGracefully();
    }
    
    public static void main(String[] args){
        ChannelFuture future = null;
        MyServer server = null;
        try{
            server = new MyServer();
            future = server.doAccept(8000);
            System.out.println("服务已启动");
            future.channel().closeFuture().sync();
        }catch(InterruptedException e){
            e.printStackTrace();
        }finally{
            if(null != future){
                try {
                    future.channel().closeFuture().sync();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            
            if(null != server){
                server.release();
            }
        }
    }
    
}

public class MyServerHandler extends ChannelHandlerAdapter {
    
    // 业务处理逻辑
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("客户端消息 : " + msg.toString());
        ctx.writeAndFlush(Unpooled.copiedBuffer("ok ".getBytes("utf8")));
    }
    // 异常处理逻辑
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        System.out.println(cause.getMessage());
        ctx.close();
    }
}

2 特殊结束符

客户端和服务器，协商定义一个特殊的分隔符号，分隔符号长度自定义。如：‘#’、‘$_$’、‘AA@’。在通讯的时候，只要没有发送分隔符号，则代表一条数据没有结束。

添加DelimiterBasedFrameDecoder特殊字符解码器并约定分隔符即可。

客户端：

this.bootstrap.handler(new ChannelInitializer<SocketChannel>() {

            @Override
            protected void initChannel(SocketChannel ch) throws Exception {
                // 定义数据分隔符
                ByteBuf delimiter = Unpooled.copiedBuffer("$E$".getBytes());
                ChannelHandler[] handlers = new ChannelHandler[3];
                handlers[0] = new DelimiterBasedFrameDecoder(1024, delimiter);
                handlers[1] = new StringDecoder(Charset.forName("UTF-8"));
                handlers[2] = new MyClientHandler();
                ch.pipeline().addLast(handlers);
            }
        });
        ChannelFuture future = this.bootstrap.connect(host, port).sync();
        return future;

服务端：

bootstrap.childHandler(new ChannelInitializer<SocketChannel>() {

            @Override
            protected void initChannel(SocketChannel ch) throws Exception {
                ByteBuf delimiter = Unpooled.copiedBuffer("$E$".getBytes());
                ChannelHandler[] acceptorHandlers = new ChannelHandler[3];
                acceptorHandlers[0] = new DelimiterBasedFrameDecoder(1024, delimiter);
                acceptorHandlers[1] = new StringDecoder(Charset.forName("UTF-8"));
                acceptorHandlers[2] = new MyServerHandler();
                ch.pipeline().addLast(acceptorHandlers);
            }
        });
        ChannelFuture future = bootstrap.bind(port).sync();
        return future;

更多看这个：Netty中解码基于分隔符的协议和基于长度的协议

3 协议

相对最成熟的数据传递方式。有服务器的开发者提供一个固定格式的协议标准。客户端和服务器发送数据和接受数据的时候，都依据协议制定和解析消息。

http协议实现看这里

Netty 实现简单的HTTP服务

构建基于Netty 的HTTP/HTTPS 应用程序