AOP auto-proxying with proxyTargetClass=true and introduction advice does not work for JDK proxy targets

[garyrussell]

See spring-projects/spring-retry#214 (comment)

Spring retry uses AOP auto proxy to add a proxy for @Retryable methods; the code unconditionally wraps the target in a new proxy. If proxyTargetClass is true (default in Spring Boot), the AbstractAutoProxyCreator does not add interfaces if the target is a JDK proxy.

if (!proxyFactory.isProxyTargetClass()) {
	if (shouldProxyTargetClass(beanClass, beanName)) {
		proxyFactory.setProxyTargetClass(true);
	}
	else {
		evaluateProxyInterfaces(beanClass, proxyFactory);
	}
}

This causes, for example, @Retryable on a spring data repository to create an invalid bean

@Repository
public interface TestRepository extends CrudRepository<Test, String> {

	@Override
	@Retryable(maxAttempts = 4)
	List<Test> findAll();

}

The inner (spring-data) proxy implements TestRepository, etc, but the outer proxy only implements the Retryable interceptor interface.

The bean 'testRepository' could not be injected as a 'com.example.demo.TestRepository' because it is a JDK dynamic proxy that implements:
	org.springframework.data.repository.CrudRepository

Although the error message is wrong (spring-projects/spring-boot#26821), it is because the proxy only implements Retryable.

Perhaps the AbstractAutoProxyCreator could detect that the target is a JDK proxy and copy the interfaces (even when proxyTargetClass) is true?

[jhoeller]

This seems to fail only in case of an introduction advice, where our fallback check in DefaultAopProxyFactory is misled into assuming that an interface has been configured (even if it was just an introduced interface), unfortunately skipping the fallback in that case. I've revised AbstractAutoProxyCreator to specifically handle JDK proxy targets in such a scenario, explicitly adding their original interfaces.