Having duplicate entries for the same classname on the classpath makes your software less stable. Depending on the order of classpath entries, which in some cases is not guaranteed, different classes may get loaded which could result in unexpected behaviour.

This plugin works by chekcking all the classes available on the classpath and if it finds more than one with the same fully qualified class name it checks the content of the classes byte by byte. If they are different it generates an error.

This applies to the classpath of the project that you add it to. I have been using this on the projects that produce a deployable and not on library type modules. Although a case can be made for adding it those as well.

It ignores duplicate classes which conflict with JDK classes.

This is based on the enforcer plugin with the same name from the Extra Enforcer Rules project: http://mojo.codehaus.org/extra-enforcer-rules/banDuplicateClasses.html

• Group dependencies when generating errors and provide an option for full listing
• Allow checks for other resource types (e.g., xml, properties)
• Provide an exclusion list of regex patterns