Transaction tran = dao.getSession().beginTransaction();总是报错

这是我的Action类/*
 * Generated by MyEclipse Struts
 * Template path: templates/java/JavaClass.vtl
 */
package com.niit.struts.action;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.hibernate.Transaction;import cn.niit.hibernate.Registration;
import cn.niit.hibernate.RegistrationDAO;import com.niit.struts.form.RegistrationForm;/** 
 * MyEclipse Struts
 * Creation date: 01-14-2008
 * 
 * XDoclet definition:
 * @struts.action path="/registration" name="registrationForm" input="/registration.jsp" scope="request" validate="true"
 * @struts.action-forward name="success" path="success.jsp" redirect="true"
 */
public class RegistrationAction extends Action {
/*
 * Generated Methods
 */ /** 
 * Method execute
 * @param mapping
 * @param form
 * @param request
 * @param response
 * @return ActionForward
 */
private RegistrationDAO dao;
public RegistrationAction(Registration dao){
setDao(new RegistrationDAO());
}
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response) {
RegistrationForm rm = (RegistrationForm) form;// TODO Auto-generated method stub
Registration regist = new Registration();
regist.setUseName(rm.getUsername());
regist.setUsePassword(rm.getUserpassword());
regist.setUseEmail(rm.getUseremail());
regist.setUsePhone(rm.getUserphone());
regist.setUseAddress(rm.getUseraddress());

RegistrationDAO dao = getDao();
Transaction tran = dao.getSession().beginTransaction();
dao.save(regist);
tran.commit();
return mapping.findForward("success");
}
public RegistrationDAO getDao() {
return dao;
}
public void setDao(RegistrationDAO dao) {
this.dao = dao;
}
}这段代码不知道哪里有错。2008-1-14 13:19:44 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet action threw exception
java.lang.InstantiationException: com.niit.struts.action.RegistrationAction
at java.lang.Class.newInstance0(Class.java:335)
at java.lang.Class.newInstance(Class.java:303)
at org.apache.struts.chain.commands.util.ClassUtils.getApplicationInstance(ClassUtils.java:71)
at org.apache.struts.chain.commands.servlet.CreateAction.createAction(CreateAction.java:98)
at org.apache.struts.chain.commands.servlet.CreateAction.getAction(CreateAction.java:68)
at org.apache.struts.chain.commands.AbstractCreateAction.execute(AbstractCreateAction.java:90)
at org.apache.struts.chain.commands.ActionCommandBase.execute(ActionCommandBase.java:51)
at org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
at org.apache.commons.chain.generic.LookupCommand.execute(LookupCommand.java:304)
at org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
at org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:283)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:263)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:584)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:595)