What does <tx:annotation-driven/> in Spring really do in the code level ?

Question

Does it set a flag in a bean ? Does it load "special" bean which then looks for @Transactional ?

Answer 1

It scans all beans in the application context and creates AOP interceptor for those which are annotated.

This is done via the SpringTransactionAnnotationParser, which is used by TransactionInterceptor - the aformentioned interceptor.

Then whenever these beans are accessed, this advice is triggered and a transaction is started before the target method is executed, and committed after the execution.