netty的decoder encoder

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<Object> out)
            throws Exception {
        decodeState = STATE_CALLING_CHILD_DECODE;
        try {
            decode(ctx, in, out);
        } finally {
            boolean removePending = decodeState == STATE_HANDLER_REMOVED_PENDING;
            decodeState = STATE_INIT;
            if (removePending) {
                handlerRemoved(ctx);
            }
        }
    }

 protected void callDecode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) {
        try {
            while (in.isReadable()) {
                int outSize = out.size();

                if (outSize > 0) {
                    fireChannelRead(ctx, out, outSize);
                    out.clear();

                    if (ctx.isRemoved()) {
                        break;
                    }
                    outSize = 0;
                }

                int oldInputLength = in.readableBytes();
                decodeRemovalReentryProtection(ctx, in, out);

                if (ctx.isRemoved()) {
                    break;
                }

                if (outSize == out.size()) {
                    if (oldInputLength == in.readableBytes()) {
                        break;
                    } else {
                        continue;
                    }
                }

                if (oldInputLength == in.readableBytes()) {
                    throw new DecoderException(
                            StringUtil.simpleClassName(getClass()) +
                                    ".decode() did not read anything but decoded a message.");
                }

                if (isSingleDecode()) {
                    break;
                }
            }
        } catch (DecoderException e) {
            throw e;
        } catch (Exception cause) {
            throw new DecoderException(cause);
        }
    }

@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