Class Not Found Issues

Permalink to this page: https://cwiki.apache.org/confluence/x/tSklBg

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: Tomcat 9.0, Tomcat 8.5, Tomcat 7.0, (historic: Tomcat 6.0).
• Don't use packageless classes and declare all imported classes!
• 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

1. Why is jsp:useBean is not working?
2. Why do I get java.lang.NoClassDefFoundError: javax/servlet/Filter?
3. Why do I get java.lang.NoClassDefFoundError: org/xml/sax/InputSource?

Answers

Why is jsp:useBean is not working?

Make sure:

• Your bean is packaged in a class.

• You have fully qualified your class name (e.g.: com.bar.package.MyClass) OR

• You have imported your class into your jsp (e.g.: <%@ page import="com.bar.package.MyClass"%> )

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

You probably have servlet-api.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-api.jar should only be found only once in $CATALINA_HOME/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.