Bug 15873

Summary: Exceptions inside an evaluated expr don't have a full stacktrace printed
Product: Taglibs Reporter: Steve Moseley <steve>
Component: Standard TaglibAssignee: Tomcat Developers Mailing List <dev>
Severity: enhancement    
Priority: P3    
Version: 1.0.1   
Target Milestone: ---   
Hardware: PC   
OS: other   

Description Steve Moseley 2003-01-07 22:53:51 UTC
When I try and retrieve the value of a property of my own custom bean, and my 
bean throws an exception, the exception message is returned and displayed but 
the stack history is lost.

I can see the code in org.apache.taglibs.standard.lang.jstl.Evaluator, where an 
ELException is caught and a JspException is thrown, and the rootCause exception 
is available, and the message is returned, but the stack trace is never passed 
up the chain.

I wasn't sure how to fix this properly, so I patched Evaluator to give me the 
stack history as follows:



   * Evaluates the expression at request time


  public Object evaluate (String pAttributeName,

			  String pAttributeValue,

			  Class pExpectedType,

			  Tag pTag,

			  PageContext pPageContext,

			  Map functions,

			  String defaultPrefix)

    throws JspException


    try {

      return sEvaluator.evaluate







    catch (ELException exc) {

    StringWriter sw = new StringWriter() ; // SRM

    PrintWriter pw = new PrintWriter(sw) ; // SRM

    exc.getRootCause().printStackTrace(pw); // SRM

    String fullStackTrace = sw.toString() ; // SRM

      throw new JspException



	  new Object [] {

	    "" + pAttributeName,

	    "" + pAttributeValue,


	    //exc.getRootCause() // SRM

        fullStackTrace // SRM




There's probably a better way to do it, perhaps?

Also, here's a simple webpage fragment that will demonstrate the problem:

<%@ page contentType="text/html" %>

<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>


  public class MyBean {

    public String throwExceptionInHere() {

      if (true) {

        throw new RuntimeException("Hey!");


	  return "";


    public String getThrowException() {

      String x = throwExceptionInHere();

      return "";





  pageContext.setAttribute("myBean", new MyBean());


<c:set var="foo" value="${myBean.throwException}" />

<c:out value="${foo}" />
Comment 1 Pierre Delisle 2003-01-10 02:04:03 UTC
Agree that it is important to expose the original exception thrown by the
web application. However, we've opted for a different
solution than the one proposed in this bug report.

The stack trace does not belong to the textual message of the exception.
However, the stack trace information should be made available.
The code in Evaluator has therefore been modified so it adds the original 
exception that occurred as the rootCause of the JspException. This 
therefore makes the original exception accessible to the container as 
a Throwable object, not just as text message.

Unless the calling code is instrumented to catch exceptions, it then becomes
the responsibility of the container to decide what should be displayed.
Unfortunately, Tomcat does not currently follow through more than 1 level
of nested root exceptions (it only displays a root cause exception defined
for ServletException). It would seem desirable for Tomcat to display rootCause
exceptions nested at deeper levels.
An RFE (see http://nagoya.apache.org/bugzilla/show_bug.cgi?id=15941) 
has been filed to that effect.