Detect invalid transaction configuration for transactional event listeners #30679
Description
Problem
It's common practice to use a simple (no custom attributes) @Transactional on methods to execute them wrapped in a transaction. Unfortunately, for methods declared as @TransactionalEventListener, this doesn't work as expected:
@Component
class SomeListener {
@Transactional
@TransactionalEventListener
void on(SomeEvent event) { /* … */ }
}Those methods are invoked in the transaction cleanup phase of an original, other transaction. This means that this particular, other transaction is still running, although in an undefined state. With a simple @Transactional declared on those methods, the code would be executed in an undefined transactional state. An obvious solution to this problem is to declare a Propagation of REQUIRES_NEW on the listener method, so that it will run in a new transaction:
@Component
class SomeListener {
@Transactional(propagation = Propagation.REQUIRES_NEW)
@TransactionalEventListener
void on(SomeEvent event) { /* … */ }
}Proposed solution
It would be nice if the erroneous arrangement shown above would be rejected, ideally at bootstrap (potentially even AOT?) time. We have to consider that a plain @Transactional is still valid in the case of the method declared to be invoked asynchronously (using @Async). In other words, a declaration like this is still valid, as the asynchronous invocation triggers the execution on a separate thread and thus a clean slate regarding transactions.
@Component
class SomeListener {
@Async
@Transactional
@TransactionalEventListener
void on(SomeEvent event) { /* … */ }
}