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
