While I was developing the Apache DS plugin for Apache Directory Studio, I ran into several class loader issues.
The Apache DS plugin defines a new Log4J appender that is used to display the logs of an Apache DS server in the a console inside Studio.
In the Apache DS plugin, the Log4J dependency is inherited from the Apache Directory Studio Jars plugin which contains the Log4J jar dependency and re-exports it in its MANIFEST.MF file.
The compilation worked fine, but at runtime I had some ClassNotFound exceptions when I was trying to create a new instance of the Logger.
Basically the problem was that the two plugins (Apache DS and Jars) are not sharing the same class loader, even if we explicitely re-export the dependency.
So, the Log4J class in the Jars plugin class loader could not find my Appender class that was in a separate class loader (the Apache DS plugin class loader).
After a few researches on google, I finaly found that I had to use the "Buddy Class Loading" feature of Eclipse to get my code working at runtime.
I though it could be interesting to share the links that helped me solve this problem if someone working on Studio faces a similar issue.