My app can't see the tag library

Question

Hi everybody,
I am developing an application in JSP which accesses an Oracle database and display the results to the user.
I am using the tag "exceltag.jar" taken from "http://www.servletsuite.com/servlets/exceltag.htm" to convert an html table to an excel sheet. This works fine on my computer but it fails after we installed the application to our web server, running Tomcat 4.1.12.
The "exceltag.jar" file has been placed under 'WEB-INF\lib' and the classpath has been set to point to that location. However when I attempt to convert the html table to an excel sheet by clicking a button, I get the following error:
java.lang.NoClassDefFoundError:
javax/servlet/jsp/tagext/BodyTagSupport at java.lang.ClassLoader.defineClass0(Native Method) at
java.lang.ClassLoader.defineClass(ClassLoader.java:509)
It seems like the application can't see the "exceltag.jar" file.
What do I need to do to overcome this problem?
Thank you very much.

Answer 1

The servlet.jar is in TOMCAT_HOME/common/lib. Since all the JARs in that directory are automatically added to the CLASSPATH and are visible to all applications running under Tomcat, you don't have to do anything for the class loader to find it.
Your app's WEB-INF/lib directory JARs are also automatically added to to the CLASSPATH. That's the correct place to put that exceltag.jar, by the way, not the TOMCAT_HOME/common/lib.
As a matter of fact, if you have a system CLASSPATH, be sure that Tomcat ignores it completely. You shouldn't even have one, IMO. (I don't.)
When I open up the servlet.jar in my TOMCAT_H0ME/common/lib, I can see a class named BodyTagSupport with path javax.servlet.jsp.tagext. You should, too.
In your exceltag.jar, you should find a TLD for the library. Open that with a text editor and make sure that the text under the <uri> tag matches that in your JSP. For example, I use the JSTL tag library. The c.tld has this <uri> tag:
  <uri>http://java.sun.com/jstl/core</uri>My JSPs that want to use the core tag library have this near the top of the page:
<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>Notice how the URIs match. That's what yours should do, too.
If you don't find a TLD inside the exceltag.jar, that means they didn't package it properly. - MOD