HTTP Status 500 - 

--------------------------------------------------------------------------------

type Exception report

message 

description The server encountered an internal error () that prevented it from fulfilling this request.

exception 

org.apache.jasper.JasperException: javax.servlet.ServletException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:522)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:398)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)


root cause 

javax.servlet.ServletException: java.lang.NullPointerException
org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:523)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:421)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:706)
org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:677)
org.apache.jsp.index_jsp._jspService(index_jsp.java:56)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)


root cause 

java.lang.NullPointerException
com.yxq.dao.DB.doPstm(DB.java:42)
com.yxq.dao.OpDB.OpClassListShow(OpDB.java:27)
com.yxq.action.IndexAction.execute(IndexAction.java:29)
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.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:706)
org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:677)
org.apache.jsp.index_jsp._jspService(index_jsp.java:56)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)


note The full stack trace of the root cause is available in the Apache Tomcat/6.0.20 logs.
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[strong]
请问这是什么原因？[/strong]
谢谢～～