Issue with NoClassDefFoundError error in a web environment Spring/Wicket/Derby/Jetty

Question

I am trying to build a simple JDBC Spring Template application, the web framework I am using is wicket and under the jetty 6 web server (through the Jetty Maven Plugin). Al

Answer 1

So the 'Could not initialize class org.apache.derby.jdbc.EmbeddedDriver' error was actually the main symptom of some other, less obvious, class loading issues.

I was using Jetty as the web server and Spring as the framework under java6.

I believe there was a class loading issue, related to the MBeanServer class.

And I did ignore an error that happened at startup: "Caused by: java.lang.LinkageError: loader constraint violation: loader (instance of org/mortbay/jetty/webapp/WebAppClassLoader) previously initiated loading for a different type with name "javax/management/MBeanServer" at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632) at java.lang.ClassLoader.defineClass(ClassLoader.java:616) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)"

I searched for the class in my WEB-INF/lib directory. It was included as part of mx4j:jar. Mx4j was a dependency for jetty-management.jar. I didn't really need jetty-management so I removed that reference from my pom file.

Basically the inclusion of MBeanServer (from mx4j) caused some kind of class loading issue where org.apache.derby.jdbc.EmbeddedDriver couldn't be loaded properly. I removed it from my web application and the application started working properly.