我写了一个计数器的程序,可是老是抱空指针的错误,运行时又是正常的,虽然可以运行,可是服务器老是报这个错,郁闷了!下面是程序:
application.jsp<%@ page language="java" contentType="text/html;charset=GB2312"%><%
    int count = 0;
    String counter_name = request.getParameter("counter_name");  //计数器名     try
    {
       count = Integer.parseInt((application.getAttribute(counter_name).toString()));
 
    }
    catch(Exception e){}
    out.println("自从应用服务器启动后,此页面已经访问了"+count+"次");
    count++;
    application.setAttribute(counter_name,new Integer(count));%>以下是使用计数器的页面
test_application.jsp<%@ page language="java" contentType="text/html;charset=GB2312"%>
<html>
  <head>
    <title>No Document</title>
    <meta-equiv="Content-Type" content="text/html;charset=gb2312">
  </head>   <body>
    测试application的页面.<br>
    <jsp:include page="application.jsp">
     <jsp:param name="counter_name" value="test_application"/>
    </jsp:include>
   </body>
</html>

解决方案 »

  1.   

    报错信息如下j
    ava.lang.NullPointerException
    at org.apache.jsp.application_jsp._jspService(application_jsp.java:61)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:390)
    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:683)
    at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:585)
    at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:505)
    at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:967)
    at org.apache.jsp.test_005fapplication_jsp._jspService(test_005fapplication_jsp.java:64)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:390)
    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:105)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:212)
    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)