Projector ClassLoader

Purpose

Summary

Allows loading classes from Projector, Projector agent and Intellij Platform without the use of reflection

Default AppClassLoader of Projector Server doesn't know anything about JB IDE and so cannot load its classes as they were loaded by different classloader. Similar, IDE ClassLoader doesn't know anything about Projector classes (and can be gathered only after IDE startup).

The idea behind ProjectorClassLoader is simple - delegate classloading to the right classloader. If we think classname determines a class from Intellij Platform then we should load it via IDE ClassLoader. If not, then we fall back to load it via AppClassLoader.

To specify how classes should be loaded with ProjectorClassLoader you need to call one of the forceLoadBy* methods:

Method Name	ClassLoader for specified class(es)
forceLoadByPlatform	AppClassLoader
forceLoadByProjectorClassLoader	ProjectorClassLoader (gather bytecode from any of AppClassLoader or IDE ClassLoader and then define class ourselves)
forceLoadByIdea	IDE ClassLoader (PathClassloader or UrlClassLoader, depending on IDE version)

Note

Another way to specify ClassLoader for class is to apply UseProjectorLoader annotation.

Initializing ProjectorClassLoader

To initialize ProjectorClassLoader, call function

package org.jetbrains.projector.server.core.classloader

fun initClassLoader(classLoader: ClassLoader): ClassLoader

somewhere at the entry point of Projector to correctly set up an instance of ProjectorClassLoader: assign IDE ClassLoader when IDE is initialized, define classes that should be force loaded via AppClassLoader or ProjectorClassLoader.

Important

Don't forget to load some other class (which will be the actual entry point for the Projector/Projector agent logic) with returned ClassLoader (if current ClassLoader is not ProjectorClassLoader) to start using ProjectorClassLoader

Currently, function is used at:

Class	Method	Reason
org.jetbrains.projector.server.ProjectorLauncher	main(args: Array<String>)	Default entry point
org.jetbrains.projector.server.ProjectorLauncher	runProjectorServer(): Boolean	Entry point for CWM
org.jetbrains.projector.agent.MainAgent	agentmain(args: String?, instrumentation: Instrumentation)	Projector Plugin entry point

Support for agent classes

Agent classes are now loaded in the same manner as regular Projector classes. However, if in the future ProjectorClassLoader will be set as a System ClassLoader, then ProjectorClassLoader needs to use appendToClassPathForInstrumentation(String jarPath) method to get the location of agent jar file. It's already implemented, so no extra work to support loading classes from agent JAR file is required.