Problem with EL returning wrong object

[Geoffrey Falk]

Hi,

I am trying to set up a simple JSP page on Tomcat 5.5.4 using JSTL-standards-1.1.2. Here is the problem I am having. I think it is a bug in commons-el.

My session scope contains an object (paginator) which has a property "itemsforpage" which returns a List:

class Paginator {
  ...
  public List getItemsforpage() {
    return items;
  }
}

I am trying to iterate over this list like this:

  <c:forEach var="item" items="${paginator.itemsforpage}">
    ....
  </c:forEach>

When I try to access the page, I am getting an exception:

29-Jan-2005 12:18:23 PM org.apache.catalina.core.ApplicationDispatcher invoke
SEVERE: Servlet.service() for servlet jsp threw exception
javax.servlet.jsp.JspTagException: Don't know how to iterate over supplied "items" in <forEach>
        at org.apache.taglibs.standard.functions.Functions.length(Unknown Source)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invokeNativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:494)
        at org.apache.commons.el.FunctionInvocation.evaluate(FunctionInvocation.java:172)
        at org.apache.commons.el.ExpressionEvaluatorImpl.evaluate(ExpressionEvaluatorImpl.java:263)
...

which says that it doesn't know how to iterate over the items I specified.
${paginator.itemsforpage}. I did some debugging and I found that the object it is dealing with is actually of type Paginator (not List)!!

It is as if I had items="${paginator}" instead of items="${paginator.itemsforpage}". However, the paginator.getItemsforpage() method is getting called.

1) Why is commons-el evaluating this expression to the wrong object? I think this is a bug.

2) Why is it using that commons-el expression evaluator (comes with Tomcat) instead of JSTL 1.1? Can I force it to use the real JSTL standards.jar?

Thanks
Geoffrey

[Geoffrey Falk]

PS I tried this with Tomcat 5.0.30 and had the same problem.

[Geoffrey Falk]

To answer my own question, in case anyone comes here with the same problem..

I found the problem. It was not the <c:forEach> tag. It was something in a completely different area of the page. I had this in my JSP:

  ${fn:length(paginator)} items on page

which is wrong because "paginator" is not a collection. I should have had:

  ${fn:length(paginator.itemsforpage)} items on page

with this it works fine.

BUT: The real problem is that the error message is extremely misleading!! The problem had nothing to do with <c:forEach>, yet the error message indicated that it did!! This cost me 6 hours of time!!!

Someone should really fix this misleading error message!!!

Grr...
Geoffrey

[Bear Bibeault]

That is odd. Thanks for posting what you discovered.

[Ben Souther]

It would be interesting to see the generated servlet code to see what really happened.