HIBERNATE运行的时候报的错误！谁能帮我一下呀？谢谢

Question

IE中报的错误内容为：java.lang.NoClassDefFoundError: org/hibernate/HibernateException
com.studytest.struts.action.AddUserAction.execute(AddUserAction.java:56)
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.doPost(ActionServlet.java:525)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)为什么找不到HIBERNATE的类？？？