jsp登录模块的问题：报错

严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
 at java.lang.String.<init>(String.java:147)
 at org.apache.jsp.checklogin_jsp._jspService(checklogin_jsp.java:87)
 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:384)
 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:687)
 at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:590)
 at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:505)
 at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:968)
 at org.apache.jsp.JSP_005finclude_jsp._jspService(JSP_005finclude_jsp.java:70)
 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:384)
 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.StandardWrapperValve.invoke(StandardWrapperValve.java:228)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
 at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
 at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
 at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
 at java.lang.Thread.run(Thread.java:619)
2012-5-18 21:27:03 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
 at java.lang.String.<init>(String.java:147)
 at org.apache.jsp.checklogin_jsp._jspService(checklogin_jsp.java:87)
 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:384)
 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:687)
 at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:590)
 at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:505)
 at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:968)
 at org.apache.jsp.JSP_005finclude_jsp._jspService(JSP_005finclude_jsp.java:70)
 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:384)
 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.StandardWrapperValve.invoke(StandardWrapperValve.java:228)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
 at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
 at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
 at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
 at java.lang.Thread.run(Thread.java:619)