正在做毕业设计，碰到一个问题，那位高手给看看是什么问题！

是一个Action!
错误提示:
HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception javax.servlet.ServletException: could not load an entity: [com.studorm.dao.Students#4]
org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:545)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:486)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:507)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause org.hibernate.exception.GenericJDBCException: could not load an entity: [com.studorm.dao.Students#4]
org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:91)
org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:79)
org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
org.hibernate.loader.Loader.loadEntity(Loader.java:1799)
org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:93)
org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:81)
org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:2730)
org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:365)
org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:346)
org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:123)
org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:177)
org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:87)
org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:891)
org.hibernate.impl.SessionImpl.get(SessionImpl.java:828)
org.hibernate.impl.SessionImpl.get(SessionImpl.java:821)
com.studorm.struts.action.DeletestudentAction.execute(DeletestudentAction.java:54)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:507)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.
--------------------------------------------------------------------------------Apache Tomcat/5.0.28程序源码：
/*
 * Generated by MyEclipse Struts
 * Template path: templates/java/JavaClass.vtl
 */
package com.studorm.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.HibernateException;
import org.hibernate.Session;
//import org.apache.commons.logging.Log;
//import org.apache.commons.logging.LogFactory;import com.studorm.dao.Students;
import com.studorm.dao.HibernateUtil;/** 
 * MyEclipse Struts
 * Creation date: 04-17-2007
 * 
 * XDoclet definition:
 * @struts.action validate="true"
 * @struts.action-forward name="deletestudentsuccess" path="/stumain.jsp"
 */
public class DeletestudentAction extends Action {
/*
 * Generated Methods
 */ /** 
 * Method execute
 * @param mapping
 * @param form
 * @param request
 * @param response
 * @return ActionForward
 */
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response){
       
// TODO Auto-generated method stub

//private static Log log = LogFactory.getLog(DeletestudentAction.class);

String id = (String)request.getParameter("student_id");

//try {
Session s = HibernateUtil.currentSession();
HibernateUtil.beginTransaction();
    Students stu = (Students)s.get(Students.class,id);
HibernateUtil.commitTransaction();
// System.out.println(stu.getId());
HibernateUtil.beginTransaction();
s.delete(stu);
HibernateUtil.commitTransaction();
HibernateUtil.closeSession();

    return (mapping.getInputForward());

/*catch (HibernateException e) {
return (mapping.findForward("deletestudentsuccess"));
} */
}
}