Mina deCode里断点 IoBuffer的POS就变了

Question

问题是:我如果在MessageDeCoderClass的decode方法的第一行,打断点,查看发现inBuffer的pos=4,导致我后面的数据全部取错.
然后,我将断点去掉.发现最后就进了正确的commandService 处理类里面.

请教为什么decode里需的pos有时候不是0呢?

用mina写了服务器,大概如下:
mina配置-server.xml: 

<bean id="ioAcceptor" class="org.apache.mina.transport.socket.nio.NioSocketAcceptor" init-method="bind" destroy-method="unbind">
    <property name="defaultLocalAddress" value=":10001" />
    <property name="handler" ref="serverHandler" />
    <property name="reuseAddress" value="true" />
    <property name="filterChainBuilder" ref="filterChainBuilder" />
  </bean>
...<bean id="codecFilter" class="org.apache.mina.filter.codec.ProtocolCodecFilter">
    <constructor-arg>
      <bean class="dc.rpc.handler.MessageCoderFactory"/>
    </constructor-arg>
  </bean><bean id="filterChainBuilder" class="org.apache.mina.core.filterchain.DefaultIoFilterChainBuilder">
    <property name="filters">
      <map>
        <entry key="executor" value-ref="executorFilter"/><entry key="mdcInjectionFilter" value-ref="mdcInjectionFilter"/>
        <entry key="codecFilter" value-ref="codecFilter"/>
        <entry key="loggingFilter" value-ref="loggingFilter"/>
      </map>
    </property>
  </bean>
.....

 解码工厂类:

public class MessageCoderFactory extends DemuxingProtocolCodecFactory{
	public MessageCoderFactory(){
		super.addMessageDecoder(MessageDeCoderClass.class);
		super.addMessageEncoder(Message.class, MessageEnCoderClass.class);
	}
}

MessageDeCoderClass:

public MessageDecoderResult decodable(IoSession session, IoBuffer buffer) {
		if(buffer.remaining() < Constant.MSG_HEAD_LENGTH)// 长量=8
			return MessageDecoderResult.NEED_DATA;
		return MessageDecoderResult.OK;
	}

public MessageDecoderResult decode(IoSession session, IoBuffer inBuffer, ProtocolDecoderOutput out)throws Exception {
		try{
			if(!isReadHead){
				head = new MessageHead();
				head.setMsgLength(inBuffer.getInt());			//与客户端沟通先发送长度,再发指令ID
				head.setCommandId(inBuffer.getInt());
			}
			if(inBuffer.remaining() < head.getMsgLength()-Constant.MSG_HEAD_LENGTH)
				return MessageDecoderResult.NEED_DATA;
			byte[] byteArray = new byte[head.getMsgLength()-Constant.MSG_HEAD_LENGTH];
			inBuffer.get(byteArray);
			isReadHead = false;
			out.write(new Message(head,IoBuffer.wrap(byteArray)));
			return MessageDecoderResult.OK;
		}catch(Exception e){
			e.printStackTrace();
			return null;
		}

Message.class

public class Message implements Serializable {
     private static final long serialVersionUID = 1L;
	/** 通信消息头部信息,用于验证,和转发消息用. 定长 */
	private MessageHead msgHead;
	/** 通信消息主体,不定长二进制流 */
	private IoBuffer msgBody;

......getter & setter...
}

MessageHead类:

public class MessageHead {
	/**消息总长度 HeadLength+bodyLength */
	private int msgLength;
	/** 指令ID */
	private int commandId;
....getter &setter.....

Handler类:

public void messageReceived(IoSession session, Object message) throws Exception {
    Message requestMsg = (Message) message;
    CommandServerInter commandService = (CommandServerInter) AppContextUtil.getCtx().getBean("loginCommand");
    if(commandService == null){
	return;
    }
    commandService.requestDeal(session, requestMsg);
}

Answer 1

在decode中，读取完head时，没有将
isReadHead设为true，导致

if(inBuffer.remaining() < head.getMsgLength()-Constant.MSG_HEAD_LENGTH)

Answer 2

在decode中，读取完head时，没有将
isReadHead设为true，导致

if(inBuffer.remaining() < head.getMsgLength()-Constant.MSG_HEAD_LENGTH)