Why do developers write Custom class loaders, why not invoke a Bootstrap class loader to invoke your custom classes? What is the need to define custom class loaders?
Depending on the application, the developers might override or completely replace the class loading mechanism to suit their needs.
For instance, I have used one application whose classes are loaded from a LDAP :S
Other apps need independent class managing ( like most of the application servers that support hot-deploy )
About resources, there are TONS, in the web, that simply cannot be listed.