public class DelimiterBasedFrameDecoder extends ByteToMessageDecoder {
随便找了一个用字符串分割粘包的decoder，继承了ByteToMessageDecoder（netty版本不同，逻辑可能有区别）
final void decodeRemovalReentryProtection(ChannelHandlerContext ctx, ByteBuf in, List
protected void callDecode(ChannelHandlerContext ctx, ByteBuf in, List
@Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { if (msg instanceof ByteBuf) { CodecOutputList out = CodecOutputList.newInstance(); try { ByteBuf data = (ByteBuf) msg; first = cumulation == null; if (first) { cumulation = data; } else { cumulation = cumulator.cumulate(ctx.alloc(), cumulation, data); } callDecode(ctx, cumulation, out); } catch (DecoderException e) { throw e; } catch (Exception e) { throw new DecoderException(e); } finally { if (cumulation != null && !cumulation.isReadable()) { numReads = 0; cumulation.release(); cumulation = null; } else if (++ numReads >= discardAfterReads) { numReads = 0; discardSomeReadBytes(); } int size = out.size(); decodeWasNull = !out.insertSinceRecycled(); fireChannelRead(ctx, out, size); out.recycle(); } } else { ctx.fireChannelRead(msg); } }
可以发现，最后是在channelRead中被调用