存根类(stub) 是什么意思？有什么作用？

  存根类是一个类，它实现了一个接口，但是实现后的每个方法都是空的。 
   

   它的作用是：如果一个接口有很多方法，如果要实现这个接口，就要实现所有的方法。但是一个类从业务来说，可能只需要其中一两个方法。如果直接去实现这个接口，除了实现所需的方法，还要实现其他所有的无关方法。而如果通过继承存根类就实现接口，就免去了这种麻烦

这个在omco2.6版本中用户登录的session中的接口就有体现。

package com.utstar.omco.jnti.inc;public interface ITBusStub extends IEngineHandle{ITAclInterface getAclInterface();void setName(String name);String getUUID();int generateSID();int getSessionCount();ITServerSession getSession(int sid);ITServerSession[] getAllSession();int delSession(int sid, ITableRegChange ic);int _onRecvResult(Msg.MsgInfo msg);Msg.MsgInfo _onNeedExec();int _onRecvFromSession(ITServerSession s, Msg.MsgInfo msg);int _onRegister(Msg.ReguestRegister reg, ITableRegChange ic);void _onUpdateRegInfo(String src, ITableRegChange ic);int _onAddSession(ITServerSession s);}

上面的类ITBusStub，就是一个stub类，它的作用主要是用于继承一个接口类，然后它的实现类只需要通过实现它这个接口就可以，

实现需要调用的方法。BusStub是它的实现类。

public class BusStub extends AbsEngineHandle implements ITBusStub,IMonitor{public static interface MsgPriorityStrategy{public int onRecvResultPriority(Msg.MsgInfo msg);public int onRecvFromSessionPriority(ITServerSession s, Msg.MsgInfo msg);}public static class ResultPriorMsgPriorityStrategy implements MsgPriorityStrategy{public int onRecvResultPriority(Msg.MsgInfo msg){return DefaultEngine.PRIO_HIGH;}public int onRecvFromSessionPriority(ITServerSession s, Msg.MsgInfo msg){return DefaultEngine.PRIO_DEFAULT;}}AtomicInteger m_curSessionIdx = new AtomicInteger(1);IMsgQueue<Msg.MsgInfo> m_cmdQue = new MsgQueue<Msg.MsgInfo>("cmd");IMsgQueue<Msg.MsgInfo> m_resultQue = new MsgQueue<Msg.MsgInfo>("result");ConcurrentHashMap<Integer, ITServerSession> m_svc = new ConcurrentHashMap<Integer, ITServerSession>();NotifyReg m_reg = new NotifyReg();ITDispatch m_dispatch;ITAclInterface m_acl = ITAclInterface.s_defaultAcl;String m_uuid = UUID.randomUUID().toString();String m_name;MsgPriorityStrategy m_msgPriorityStrategy;LongStatPrp sp_cmdnum = new LongStatPrp("recv cmd",0);LongStatPrp sp_resultnum = new LongStatPrp("send result",0);LongStatPrp sp_notifynum = new LongStatPrp("send notify",0);private static final Log logger = LogFactory.getLog("comm");public BusStub(String name){this(name, null);}public BusStub(String name, MsgPriorityStrategy msgPriorityStrategy){m_name = name;m_msgPriorityStrategy = msgPriorityStrategy;}public String getName(){return m_name;}public void setName(String name){m_name = name;}public String getUUID(){return m_uuid;}