Wishlist

Revision as of 11:32, 17 November 2006

Custom ClassLoaders for Modules

OpenCms should provide its own ClassLoader for each module.

• The Module ClassLoader is instantiated along with the module and used to load classes, classpath resources and libraries contained in the module directly from VFS.
• The classpath of a Module ClassLoader contains
  • /system/modules/<modulename>/classes/
  • /system/modules/<modulename>/lib/*.jar
• Module dependencies make up a Module ClassLoader hierarchy. If module B depends on module A, the Module ClassLoader of B has the Module ClassLoader of A as a parent, thereby making A's classpath available to B.
• The Module ClassLoader of a module which does not depend on a different module has the standard Webapp ClassLoader as its parent.
• When a class should be loaded, the Module ClassLoader first looks into the module classpath. If it does not find the class there it delegates class loading to its parent.
• Each time OpenCms detects that a file on the Module ClassLoader classpath changes, the Module ClassLoader is thrown away and a new instance is created.

Benefits:

• No need to export files from the VFS to WEB-INF/lib and WEB-INF/classes.
• It is no longer required to reload OpenCms for each change to a module classpath file.
• Ability to use different and incompatible versions of libraries in different modules.

Open Questions: How would the Module ClassLoader perform JSP loading?