$JAXBAccessorF_ and $JAXBAccessorM_ cache loosing classes and failing to re-create classes.

The JAXB implementation contains a package of classes to optimise field and method access by dynamically generating classes to avoid reflection, this has a start-up performance hit but then leads to an optimised runtime.

The package is: -

'com.sun.xml.bind.v2.runtime.reflect.opt'

Within the Injector class is a HashMap to maintain a cache of these classes against the classloader they were created for: -

private static final Map<ClassLoader,WeakReference<Injector>> injectors =
Collections.synchronizedMap(new WeakHashMap<ClassLoader,WeakReference<Injector>>());

A WeakReference has been used to wrap the value to prevent the value retaining a reference to the ClassLoader and then preventing garbage collection and leading to a leak.

The problem is that nothing retains a reference to the Injector so as this is wrapped with a WeakReference it is garbage collected.

I will attach to this case a new version of Injector.java.

The fix switches to using a Strong reference to the Injector so it is not garbage collected.

To maintain the original requirements the Injector will no longer hold a reference to the ClassLoader and will instead make use of the one passed in.

Within the Injector the HashMap of classes will reference the Class with a WeakReference. If we get a WeakReference with no class it means the class was previously loaded but garbage collected, in this case try to load the class by name from the classloader - if this fails then redefine the class.