好长的异常，帮忙看看

Question

找了成天，java.lang.NullPointerException这个都不知道在哪里发生了，
程序主要是从servlet UpdataStudent处理完一些东西然后forward到servlet Find_XY_ZY_BJ  然后forward到一个jsp页面
我从错误中定位是，它总是定位在
UpdataStudent 的  req.getRequestDispatcher("/findxyzybj").forward(req, res);
Find_XY_ZY_BJ 的
req.getRequestDispatcher("/frame/xinxixiugai/xsxg.jsp?ta=y").forward(req,res);但我在程序中走了好几遍，都没有发现有NullPointerException的情况？
恳求各位帮忙看看到底那些情况导致的？2008-10-26 18:40:54 org.apache.catalina.core.ApplicationDispatcher invoke
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.frame.xinxixiugai.xsxg_jsp._jspService(xsxg_jsp.java:300)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:445)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:379)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:292)
at cn.xuejiguanli.servlet.student.Find_XY_ZY_BJ.doGet(Find_XY_ZY_BJ.java:82)
at cn.xuejiguanli.servlet.student.Find_XY_ZY_BJ.doPost(Find_XY_ZY_BJ.java:105)
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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:445)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:379)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:292)
at cn.xuejiguanli.servlet.student.UpdataStudent.doGet(UpdataStudent.java:227)
at cn.xuejiguanli.servlet.student.UpdataStudent.doPost(UpdataStudent.java:257)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at 
        onHandler.process(Http11Protocol.java:581)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Unknown Source)
2008-10-26 18:40:54 org.apache.catalina.core.ApplicationDispatcher invoke
严重: Servlet.service() for servlet Find_XY_ZY_BJ threw exception
java.lang.NullPointerException
at org.apache.jsp.frame.xinxixiugai.xsxg_jsp._jspService(xsxg_jsp.java:300)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:445)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:379)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:292)
at cn.xuejiguanli.servlet.student.Find_XY_ZY_BJ.doGet(Find_XY_ZY_BJ.java:82)
at cn.xuejiguanli.servlet.student.Find_XY_ZY_BJ.doPost(Find_XY_ZY_BJ.java:105)
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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:445)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:379)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:292)
at cn.xuejiguanli.servlet.student.UpdataStudent.doGet(UpdataStudent.java:227)
at cn.xuejiguanli.servlet.student.UpdataStudent.doPost(UpdataStudent.java:257)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

2008-10-26 18:40:54 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet UpdataStu threw exception
java.lang.NullPointerException
at org.apache.jsp.frame.xinxixiugai.xsxg_jsp._jspService(xsxg_jsp.java:300)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:445)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:379)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:292)
at cn.xuejiguanli.servlet.student.Find_XY_ZY_BJ.doGet(Find_XY_ZY_BJ.java:82)
at cn.xuejiguanli.servlet.student.Find_XY_ZY_BJ.doPost(Find_XY_ZY_BJ.java:105)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at 

Answer 1

这个NullPointerException发生在frame/xinxixiugai/xsxg.jsp文件中，检查一下看看

Answer 2

java.lang.NullPointerException 
at org.apache.jsp.frame.xinxixiugai.xsxg_jsp._jspService(xsxg_jsp.java:300) 楼上说得对
实在看不出，就到work目录下的xsxg_jsp.java文件第300行

Answer 3

到work目录下看看xsxg_jsp.java的源码应该会找到的快点.

Answer 4

 req.getRequestDispatcher("/frame/xinxixiugai/xsxg.jsp?ta=y").forward(req,res); 
先改成一个别页面看看能不跳过去，
能的话，再到出NULL的地方看一下。request中值只能转一次，下次转之前，确认传值了。

Answer 5

(xsxg_jsp.java:300)这里有问题，可以用if(xxx!=null)试一下