Instrumenting classloader to transform classes before being instantiated

[young_matthewd]

Using Spring 3.1+

Is it possible to get at the Application context loader's classloader to transform a Class definition? Seen the weaving instrumentation stuff but haven't found a solid example online. Not sure how Spring handles class loading but assuming the application context is a "common" shareholder for classes in the classpath and any child classloader (made for whatever reasons) has the App context as it's parent.

What I want to do is intercept the registration of or reload certain classes to add a field with a specific annotation.

Looks like the @EnableLoadTimeWeaving allows for setting up a private LoadTimeWeavingConfigurer. Just not sure what to use. Testing is done in Eclipse but the target environment will not be forced into a particular container (i.e. Weblogic, Tomcat and so forth). Would like to not use the -javaagent to jack in a LoadTimeWeaver which is what I assume the EnableLoadTimeWeaving does? Should be able to add a transformer that switches out my bytecode.

Ideas?

[young_matthewd]

Tried using @EnableLoadTimeWeaving as follows

....
@@EnableLoadTimeWeaving
public class ApplicationConfig implements LoadTimeWeavingConfigurer {
...

@Override
public LoadTimeWeaver getLoadTimeWeaver() {
LoadTimeWeaver ltw = new SimpleLoadTimeWeaver();

ltw.addTransformer(new ClassFileTransformer() {

@Override
public byte[] transform(ClassLoader loader, String className,
Class<?> classBeingRedefined,
ProtectionDomain protectionDomain, byte[] classfileBuffer)
throws IllegalClassFormatException {
System.out.println("Transformer to Transform Class: "
+ className);
return classfileBuffer;
}
});
return ltw;
}

But the transform method never gets called.