《netty权威指南》私有协议栈开发中代码问题

1.这里设置字段长度，要减报文头长度和长度值字段的长度所以要减8

 byteBuf.setInt(4,byteBuf.readableBytes() - 8 );

下面是改后的源码

public class NettyMessageEncoder extends MessageToByteEncoder {

    MarshallingEncoder marshallingEncoder;

    public NettyMessageEncoder() throws IOException {
        this.marshallingEncoder = new MarshallingEncoder();
    }

    protected void encode(ChannelHandlerContext channelHandlerContext, NettyMessage nettyMessage, ByteBuf byteBuf)
            throws Exception {
        if (nettyMessage == null || nettyMessage.getHeader() == null) {
            throw new Exception("The encode message is null");
        }
        byteBuf.writeInt(nettyMessage.getHeader().getCrcCode());
        byteBuf.writeInt(nettyMessage.getHeader().getLength());
        byteBuf.writeLong(nettyMessage.getHeader().getSessionID());
        byteBuf.writeByte(nettyMessage.getHeader().getType());
        byteBuf.writeByte(nettyMessage.getHeader().getPriority());
        byteBuf.writeInt(nettyMessage.getHeader().getAttachment().size());
        String key = null;
        byte[] keyArray = null;
        Object value = null;
        for (Map.Entry param : nettyMessage.getHeader().getAttachment().entrySet()) {

            key = param.getKey();
            keyArray = key.getBytes("UTF-8");
            byteBuf.writeInt(keyArray.length);
            byteBuf.writeBytes(keyArray);
            value = param.getValue();
            marshallingEncoder.encode(value, byteBuf);
        }
        if (nettyMessage.getBody() != null) {
            marshallingEncoder.encode(nettyMessage.getBody(), byteBuf);
        } else {
            byteBuf.writeInt(0);

        }
        byteBuf.setInt(4,byteBuf.readableBytes() - 8 );
    }

}