[Tomcat Wiki] Update of "FAQ/Class Not Found" by GianlucaVarisco

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The following page has been changed by GianlucaVarisco:
http://wiki.apache.org/tomcat/FAQ/Class_Not_Found

The comment on the change is:
FAQ Migration - Issue 20 - GHOP Contest

New page:
== Class Not Found Issues ==

=== Preface ===

This page discusses the various ways you see Class Not Found errors or very similar errors. It is strongly advised you read the following topics:

    * Classloader HOWTO pages:  [http://tomcat.apache.org/tomcat-4.1-doc/class-loader-howto.html Tomcat 4.1],  [http://tomcat.apache.org/tomcat-5.0-doc/class-loader-howto.html Tomcat 5.0],  [http://tomcat.apache.org/tomcat-5.5-doc/class-loader-howto.html Tomcat 5.5].
    * [http://marc.theaimsgroup.com/?t=104317529200004&r=1&w=2 Don't] [http://marc.theaimsgroup.com/?t=104380440100003&r=1&w=2 use] [http://marc.theaimsgroup.com/?t=96947656900002&r=1&w=2 packageless] [http://marc.theaimsgroup.com/?t=104491020100002&r=1&w=2 classes] [http://marc.theaimsgroup.com/?t=104265576200003&r=1&w=2 and] [http://marc.theaimsgroup.com/?t=104249748300001&r=1&w=2 declare] [http://marc.theaimsgroup.com/?t=102996950100003&r=1&w=2 all] [http://marc.theaimsgroup.com/?t=102922189400001&r=1&w=2 imported classes]!
    * [http://marc.theaimsgroup.com/?l=tomcat-user&m=103843452413727&w=2 Another answer to a classloader issue]

If you get a NoClassDefFoundError exception, the root cause might be the same as for a ClassNotFound exception.

=== Questions ===

* '''Why is jsp:useBean is not working?'''

Make sure:

    * Your bean is packaged in a class.
    * You have fully qualified your class name (eg:com.bar.package.MyClass) OR
    * You have imported your class into your jsp (eg: <%@ pageimport="com.bar.package.MyClass"%>)

* '''Why do I get java.lang.NoClassDefFoundError: javax/servlet/Filter?'''

You probably have servlet.jar floating around somewhere it shouldn't be. This really messes up the classloaders since Tomcat's classloaders don't act quite as normal as one expects (see links above). servlet.jar should only be found only once in $CATALINA_HOME/common/lib.

* '''Why do I get java.lang.NoClassDefFoundError: org/xml/sax/InputSource?'''

You have conflicting XML api jar files in your classpath. Read the README or RELEASE-NOTES for more information. 

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