Make TransactionalApplicationListenerAdapter support fallbackExecution

spring-tx/src/main/java/org/springframework/transaction/event/TransactionalApplicationListener.java

@@ -43,6 +43,7 @@
  *
  * @author Juergen Hoeller
  * @author Oliver Drotbohm
+ * @author Réda Housni Alaoui
  * @since 5.3
  * @param <E> the specific {@code ApplicationEvent} subclass to listen to
  * @see TransactionalEventListener
@@ -134,10 +135,26 @@ static <T> TransactionalApplicationListener<PayloadApplicationEvent<T>> forPaylo
 	 */
 	static <T> TransactionalApplicationListener<PayloadApplicationEvent<T>> forPayload(
 			TransactionPhase phase, Consumer<T> consumer) {
+		return forPayload(phase, false, consumer);
+	}
+
+	/**
+	 * Create a new {@code TransactionalApplicationListener} for the given payload consumer.
+	 * @param phase the transaction phase in which to invoke the listener
+	 * @param fallbackExecution Whether the event should be handled if no transaction is running.
+	 * @param consumer the event payload consumer
+	 * @param <T> the type of the event payload
+	 * @return a corresponding {@code TransactionalApplicationListener} instance
+	 * @see PayloadApplicationEvent#getPayload()
+	 * @see TransactionalApplicationListenerAdapter
+	 */
+	static <T> TransactionalApplicationListener<PayloadApplicationEvent<T>> forPayload(
+			TransactionPhase phase, boolean fallbackExecution, Consumer<T> consumer) {
 
 		TransactionalApplicationListenerAdapter<PayloadApplicationEvent<T>> listener =
 				new TransactionalApplicationListenerAdapter<>(event -> consumer.accept(event.getPayload()));
 		listener.setTransactionPhase(phase);
+		listener.setFallbackExecution(fallbackExecution);
 		return listener;
 	}
 

spring-tx/src/main/java/org/springframework/transaction/event/TransactionalApplicationListenerAdapter.java

@@ -19,6 +19,8 @@
 import java.util.List;
 import java.util.concurrent.CopyOnWriteArrayList;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationListener;
 import org.springframework.core.Ordered;
@@ -35,6 +37,7 @@
  * as a convenient alternative to custom usage of this adapter class.
  *
  * @author Juergen Hoeller
+ * @author Réda Housni Alaoui
  * @since 5.3
  * @param <E> the specific {@code ApplicationEvent} subclass to listen to
  * @see TransactionalApplicationListener
@@ -44,11 +47,14 @@
 public class TransactionalApplicationListenerAdapter<E extends ApplicationEvent>
 		implements TransactionalApplicationListener<E>, Ordered {
 
+	private final Log logger = LogFactory.getLog(getClass());
+
 	private final ApplicationListener<E> targetListener;
 
 	private int order = Ordered.LOWEST_PRECEDENCE;
 
 	private TransactionPhase transactionPhase = TransactionPhase.AFTER_COMMIT;
+	private boolean fallbackExecution;
 
 	private String listenerId = "";
 
@@ -97,6 +103,13 @@ public TransactionPhase getTransactionPhase() {
 		return this.transactionPhase;
 	}
 
+	/**
+	 * @param fallbackExecution Whether the event should be handled if no transaction is running.
+	 */
+	public void setFallbackExecution(boolean fallbackExecution) {
+		this.fallbackExecution = fallbackExecution;
+	}
+
 	/**
 	 * Specify an id to identify the listener with.
 	 * <p>The default is an empty String.
@@ -127,7 +140,23 @@ public void processEvent(E event) {
 
 	@Override
 	public void onApplicationEvent(E event) {
-		TransactionalApplicationListenerSynchronization.register(event, this, this.callbacks);
+		if (TransactionalApplicationListenerSynchronization.register(event, this, this.callbacks)) {
+			if (logger.isDebugEnabled()) {
+				logger.debug("Registered transaction synchronization for " + event);
+			}
+		}
+		else if (fallbackExecution) {
+			if (getTransactionPhase() == TransactionPhase.AFTER_ROLLBACK && logger.isWarnEnabled()) {
+				logger.warn("Processing " + event + " as a fallback execution on AFTER_ROLLBACK phase");
+			}
+			processEvent(event);
+		}
+		else {
+			// No transactional event execution at all
+			if (logger.isDebugEnabled()) {
+				logger.debug("No transaction is active - skipping " + event);
+			}
+		}
 	}
 
 }

spring-tx/src/test/java/org/springframework/transaction/event/TransactionalApplicationListenerAdapterTests.java

@@ -25,8 +25,11 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatRuntimeException;
 
+import java.util.concurrent.atomic.AtomicReference;
+
 /**
  * @author Juergen Hoeller
+ * @author Réda Housni Alaoui
  */
 class TransactionalApplicationListenerAdapterTests {
 
@@ -88,6 +91,44 @@ void useSpecifiedIdentifier() {
 		assertThat(adapter.getListenerId()).isEqualTo("identifier");
 	}
 
+	@Test
+	void invokesNothingOutsideOfTransaction() {
+		CapturingSynchronizationCallback callback = new CapturingSynchronizationCallback();
+		PayloadApplicationEvent<Object> event = new PayloadApplicationEvent<>(this, new Object());
+
+		AtomicReference<Object> consumedPayload = new AtomicReference<>();
+		TransactionalApplicationListener<PayloadApplicationEvent<Object>> adapter =
+				TransactionalApplicationListener.forPayload(consumedPayload::set);
+		adapter.addCallback(callback);
+		adapter.onApplicationEvent(event);
+
+		assertThat(consumedPayload.get()).isNull();
+		assertThat(callback.preEvent).isNull();
+		assertThat(callback.postEvent).isNull();
+		assertThat(callback.ex).isNull();
+		assertThat(adapter.getTransactionPhase()).isEqualTo(TransactionPhase.AFTER_COMMIT);
+		assertThat(adapter.getListenerId()).isEmpty();
+	}
+
+	@Test
+	void invokesConsumerOutsideOfTransactionIfFallbackExecutionEnabled() {
+		CapturingSynchronizationCallback callback = new CapturingSynchronizationCallback();
+		PayloadApplicationEvent<Object> event = new PayloadApplicationEvent<>(this, new Object());
+
+		AtomicReference<Object> consumedPayload = new AtomicReference<>();
+		TransactionalApplicationListener<PayloadApplicationEvent<Object>> adapter =
+				TransactionalApplicationListener.forPayload(TransactionPhase.AFTER_COMMIT, true, consumedPayload::set);
+		adapter.addCallback(callback);
+		adapter.onApplicationEvent(event);
+
+		assertThat(consumedPayload.get()).isSameAs(event.getPayload());
+		assertThat(callback.preEvent).isNull();
+		assertThat(callback.postEvent).isNull();
+		assertThat(callback.ex).isNull();
+		assertThat(adapter.getTransactionPhase()).isEqualTo(TransactionPhase.AFTER_COMMIT);
+		assertThat(adapter.getListenerId()).isEmpty();
+	}
+
 
 	private static void runInTransaction(Runnable runnable) {
 		TransactionSynchronizationManager.setActualTransactionActive(true);