Maven plugin execution isolation

Maven2 takes advantage of Plexus' ability to execute a component using a ClassWorlds ClassRealm that is populated with the JAR containing the component in question and all of its dependencies. Using ClassWorlds notation for realms we have the following:

      [plexus.core]
            ^
            |
   [plexus.core.maven]
     ^            ^
     |            |
[plugin0]      [plugin1]

The plexus.core realm contains the resources required to run any plexus application; The plexus.core.maven realm contains all of the resources required to run Maven. Each subsequent plugin realm contains the JAR plugin as well as its dependencies. The realms noted above are setup in a hierarchical structure where the resources in the parent realms are available but the realm is searched first before a search is made in the parent realm.

Plugins are guaranteed to be provided the resources found in plexus.core and plexus.core.maven realms at run-time if required. Plugins can state compile-time dependencies on any of the resources found in the core realms listed above and these dependencies will be included in the plugin descriptor that is generated but when running within Maven these resources will be filtered out. In other words these resources will not be added the realm created for the plugins execution as they are provided in the parent realms.