Proxy creation improvements for JPMS, remove the need for --add-opens in some cases #25132
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The best way to define a class is to define using an anchor class, which defines its classloader and security policies, and is the only way to define a class in Java 9+ without --add-opens on the command line. The package name of the anchor class must be the same as the new class. If the conditions are not met, we fall back to calling private methods on the ClassLoader to define classes. This needs --add-opens, otherwise a exception is raised. Moved global references to the private ClassLoader methods to a separate ClassLoaderMethods class. This means that the global references will be initialized lazily only when needed, to avoid getting an exception on accessing the private methods (if not --add-opens, e.g. in GF Embedded) if they are not needed.
Weld specifies a different package name for proxies than for the original class. We change the name of the proxy class using Javassist to keep the original package name so that we can use the Lookup method. We keep separate Javassist class pools for separate application classloaders, so that applications don't share them.
Discovered a flaw in the solution for ProxyServiceImpl
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Raising as a draft, because this improves only a few places. Hopefully all tests pass and we can add more improvements gradually.
In short, use JPMS compatible MethodHandles.Lookup instead of calling ClassLoader.defineClass by reflection. This approach has some limitations. We need a class to be used as a template (the generated class will have the same classloader and protection domain derived from it). And the generated class must have the same package name as the template class.
For Weld proxies, I decided to generate a class with a different name than Weld requests, because the generated class must be in the same package as the anchor class and Weld requests a different package name for the generated classes. It looks like Weld doesn't care and all worked on my sample app with EJBs.
Ideally, all methods in
ClassGeneratorthat I marked as deprecated, will be removed and callers will be refactored to use the non-deprecated methods. The deprecated methods use reflection incompatible with JPMS, the other ones use the JPMS compatible MethodHandles. There are still a lot of places, though, where the deprecated methods are used, so it will take some time.Yet to refactor:
ProxyServicesImpl.classPoolMapshould be moved to a global service rather than be a static field. It must be global becauseProxyServicesImplis created for each app deployment, while the classloader where the classes are generated, is shared. So the cache needs to be preserved, otherwise we'd attempt to create a new class that already exists in the classloader.