Classloader/Servlet engine problems

Question

I am running across a problem that I believe is related to the Classloaders being used.
If a class in the application server classpath references classes that are loaded by an individual web application, I get a ClassNotFoundException. From what I understand, the application server uses a separate Classloader for each web application.
Let's say I have 2 classes. Class A which references Class B. If I instantiate a classloader and load Class A then later instantiate another classloader and load class B (assume Class A's classloader doesn't have class B in it's classpath), should Class A be able to see Class B at runtime?

Answer 1

A ClassLoader can load any class that it can resolve, regardless of the behavior of other ClassLoaders. So, if your ClassLoader can not load a particular class that is being loaded by the web application, then either a) there is a class path issue or b) the web application is using a specialized method for loading classes which is not visible to your ClassLoader, thus preventing you from loading the classes.
Logic within a subclass of ClassLoader is only executed after the parent class fails to load a particular class. So, the ClassLoader for the web application might implement findClass(String) in a way that allows it to find classes that your ClassLoader will never find. Look at the javadoc comments on ClassLoader, espically load(String, boolean) which explains the process for how each class is loaded... .... hopefully this information helps. Take care.