Javassist NotFoundException when getting java.io.Serializable with JDK9

Question

I have the following code:

private static CtClass resolveCtClass(String clazz) throws NotFoundException {
  ClassPool pool = ClassPool.getDefault();
  return pool.get( clazz );
}

When running under JDK8, if this method is called using java.io.Serializable, it works, but when running under the JDK9 environment, it throws the NotFoundException.

Is there something I overlooked here?

Answer 1

This does no longer happen with the current EA builds of Java 9. Class files are now always locatable even if they are encapsulated in a module.

This is a consequence of Java 9's module encapsulation where non-exported resources are no longer available via the ClassLoader API. Under the covers, Javassist calls

ClassLoader.getSystemClassLoader().findResource("java/io/Serializable.class");

to get hold of the class file for Serializable. It then parses this class file and represents the information similarly to the Java reflection API but without loading the class such that it can be edited prior to loading it.

Until Java 8, this class file was accessible as most class loaders rely on looking up a class file before loading it such that the above call returned a URL pointing to the file. Since Java 9, resources of named modules are only available via the new API method findResource(String, String) where the second arguments names the module of that class.

The short answer is: Javassist does no longer work with Java 9 and none of its dependant projects will. This is a known issue with the current Java 9 implementation and will hopefully be fixed prior to release.

Answer 2

(I never used Javassist so I'm just shooting in the dark, here...)

The documentation of ClassPool says:

If get() is called on this object, it searches various sources represented by ClassPath to find a class file and then it creates a CtClass object representing that class file.

This seems to be bound to the concept of the class path. Looking at ClassPath and CtClass supports that assumption.

If that is the case, then Javassist might just not be fit to look into JDK 9's brand new modules.

If my guess is correct, you should not be able to get any JDK class from the pool. This should be easily verifiable.