Processing custom annotations with a CDI extension and Javassist

[oscarcs]

Hello,

I am trying to modify the bytecode of some classes marked with a custom annotation when the application starts.

If I am correct, the only way to do this is:

1. Using a DeploymentUnitProcessor.

2. Using a CDI extension.

I think the second one is more portable and easy to implement so I have made a little prototype application (EAR) that includes one jar with the classes to process and another one with the CDI extension. It seems to scan and find the annotated classes successfully, but when I try to use de javassist ClassPool get method to retrieve the annotated class it throws a "javassit.NotFoundException".

This is the problematic code snnipet:

...   
<T> void processAnnotatedType(@Observes ProcessAnnotatedType<T> pat, BeanManager beanManager) {
        try {
             // If the annotation is present...
            Class<? extends Annotation> clazz = (Class<? extends Annotation>)Class.forName("mypackage.MyAnnotation");
            if(pat.getAnnotatedType().isAnnotationPresent(clazz)) {

                    // Get the annotated class name
                    String className = pat.getAnnotatedType().getJavaClass().getName();

                    // This is only a test to confirm that the class is located in the classpath
                    // And it works!!!
                    Class targetClass = Class.forName(className);

                    ClassPool cp = ClassPool.getDefault();

                    // But this throws a javassit.NotFoundException. Why???
                    CtClass cc = cp.get(className);

            }
        }
        catch(Exception e) {
            throw new RuntimeException("Error processing annotation", e);
        }
    }
...

Can somebody please tell me what I may be doing wrong?

Thanks in advance.

- Oscar

[evantill]

Try adding this line :

ClassPool cp = ClassPool.getDefault();
pool.insertClassPath(new ClassClassPath(this.getClass()));

Have a look on this page http://www.csg.is.titech.ac.jp/~chiba/javassist/tutorial/tutorial.html

[oscarcs]

You were correct. It works. Thanks a lot!.

But I have discovered that the CDI approach is not valid for me because i am trying to process some JPA entities that seem to be loaded before by JPA/Hibernate so when i try to modify them it's to late: they are present on the classloader.

So i have taken the other way: i have written a JBoss extension with a DeploymentUnitProcessor and it seems to work fine, except that again i have no idea of how to get the classpath from the DeploymentPhaseContext. I can get the classloader like this:

phaseContext.getDeploymentUnit().getAttachment(Attachments.MODULE).getClassLoader()

but i don't know what's the next step.

Finally, i have some doubts about how it will perform taking in account that hibernate is also doing some "magic" on this clases.

[evantill]

Depending on what goal you are trying to achieve (could you explain a bit more ?) :

I would try to forget the byte code manipulation and go ahead with interceptors (in your CDI extension)

Or continue in bytecode manipulation direction and wrap the annotation type to return the modified bytecode.

To do so, overrid the getJavaClass() method (see Wrapping an AnnotatedType in http://docs.jboss.org/weld/reference/latest/en-US/html/extend.html#d0e5057)