hibernate报错，我是初学，看不懂错误是什么引起的，请大家帮忙看一下

java.lang.NoClassDefFoundError: org/hibernate/Session
com.test.lt.action.RegistAction.execute(RegistAction.java:54)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:419)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)分有点少，对不住了，我现在没有多少分了