【Netty】使用解码器Decoder解决TCP粘包和拆包问题

解码器Decoder和ChannelHandler的关系

netty的解码器通常是继承自ByteToMessageDecoder，而它又是继承自ChannelInboundHandlerAdapter，其实也是一种ChannelHandler和我们自定义的ChannelHandler一样都是来处理进入或者出去的数据。常用的几种解码器有：

LineBasedFrameDecoder

DelimiterBasedFrameDecoder

FixedLengthFrameDecoder

LineBasedFrameDecoder

LineBasedFrameDecoder 行解码器，遍历ByteBuf中的可读字节，按行（\n \r\n）处理

StringDecoder

StringDecoder将接受的码流转换为字符串

代码中使用 @Override protected void initChannel(SocketChannel ch) throws Exception { ChannelPipeline pipeline = ch.pipeline(); //LineBasedFrameDecoder遍历ByteBuf中的可读字节，按行（\n \r\n）处理 pipeline.addLast(new LineBasedFrameDecoder(1024)); //StringDecoder将接受的码流转换为字符串 pipeline.addLast(new StringDecoder()); pipeline.addLast(new NettyServerHandler()); }

NettyServerHandler处理类中读取,String message = (String) msg;直接转换为String：

private int count = 0; @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { String message = (String) msg; LOGGER.info("client received message {}：{}", ++count, message); } DelimiterBasedFrameDecoder

DelimiterBasedFrameDecoder,将特定分隔符作为码流结束标志的解码器。

代码中使用 @Override protected void initChannel(SocketChannel ch) throws Exception { ChannelPipeline pipeline = ch.pipeline(); ByteBuf byteBuf = Unpooled.copiedBuffer("$_".getBytes()); pipeline.addLast(new DelimiterBasedFrameDecoder(1024,true,true,byteBuf)); pipeline.addLast(new StringDecoder()); pipeline.addLast(new NettyServerHandler()); } FixedLengthFrameDecoder

FixedLengthFrameDecoder 固定长度解码器，只会读取指定长度的码流。

代码中使用 @Override protected void initChannel(SocketChannel ch) throws Exception { ChannelPipeline pipeline = ch.pipeline(); pipeline.addLast(new FixedLengthFrameDecoder(24)); pipeline.addLast(new StringDecoder()); pipeline.addLast(new NettyServerHandler()); }