NoClassDefFoundError

Symptom: "NoClassDefFoundError: com/atlassian/jira/gadgets/system/AbstractResource"

Cause: a plugin is lazily instantiated and then fails to find a needed class

Solution: make sure the class and package name are correct and that the class is declared as a component in its atlassian-plugin.xml.

Simple Example:

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2010-02-23 13:17:10,611 http-8080-Processor19 ERROR admin 47830x17x3 1bvaudl 
http://localhost:8080/rest/gadget/1.0/stats/generate [atlassian.plugin.servlet.DefaultServletModuleManager] Unable to create filter
com.atlassian.plugin.servlet.util.LazyLoadedReference$InitializationException: java.lang.NoClassDefFoundError: com/atlassian/jira/gadgets/system/AbstractResource
    at com.atlassian.plugin.servlet.util.LazyLoadedReference.get(LazyLoadedReference.java:94)
...

In this case, the class using AbstractResource class was in the wrong package. Unfortunately, the name of the actual class in the plugin that required the missing class does not appear in the log file.

A More Complex Example

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2010-02-23 16:20:22,917 http-8080-Processor25 ERROR admin 58822x1x1 17hs118 
http://localhost:8080/rest/example/1.0/myplugin [atlassian.plugin.servlet.DefaultServletModuleManager] Unable to create filter
com.atlassian.plugin.servlet.util.LazyLoadedReference$InitializationException: java.lang.NoClassDefFoundError: com/atlassian/jira/gadgets/system/SearchQueryBackedResource
    at com.atlassian.plugin.servlet.util.LazyLoadedReference.get(LazyLoadedReference.java:94)
...

In this case, the SearchQueryBackedResource class was not exported by the atlassian-plugin.xml file. The workaround is to copy the required class (and all the classes it requires in turn) to your gadget source tree. Alternatively JRA-18986 recommends creating a simple class in your plugin that wraps the core JIRA class and just calls super().