Spring Fall back from cglib to JDK proxies when possible

I am using Spring Boot 2.7, which defaults to cglib proxies. I have a JavaConfig bean definition:

interface ServiceInterface {
  @Async void log()
}

@Bean
ServiceInterface myBean() {
  new Impl()
}

If the Impl class is not subclassable by cglib (in this case, it uses a static factory method and has a private constructor), context startup fails with a "cglib can't subclass" error. However, if the declared bean type is an interface, in my view the ProxyFactory ought to use a JDK proxy instead (in the first place, but certainly if cglib fails).

Comment From: YongGoose

I’ve implemented the changes in this PR. (#35344)

When a CodeGenerationException or IllegalArgumentException occurs, the logic now falls back to using a JDK Dynamic Proxy. I tested it with a class that has a private constructor, and the exception that used to occur no longer happens.

I also have an additional idea.

What about adding an attribute like fallbackToJdkProxy to the @EnableAspectJAutoProxy annotation? If the attribute is set to true, the logic would fall back to a JDK dynamic proxy. If it’s false, the current behavior (throwing an exception) would remain unchanged.

This way, users can decide whether or not to enable this feature, which seems like a good approach.

If this sounds reasonable, I’d like to work on it in a separate PR 🚀