GH-305 - Multicaster now honors listener condition.

We now reflectively invoke ApplicationListenerMethodAdapter.shouldHandle(…) when selecting event listeners to make sure that conditions defined in, for example, @TransactionalEventListener are considered before registering an event publication.

Author: odrotbohm

spring-modulith-events/spring-modulith-events-core/src/main/java/org/springframework/modulith/events/support/PersistentApplicationEventMulticaster.java

@@ -15,6 +15,7 @@
  */
 package org.springframework.modulith.events.support;
 
+import java.lang.reflect.Method;
 import java.util.Collection;
 import java.util.List;
 import java.util.function.Consumer;
@@ -29,17 +30,20 @@
 import org.springframework.context.PayloadApplicationEvent;
 import org.springframework.context.event.AbstractApplicationEventMulticaster;
 import org.springframework.context.event.ApplicationEventMulticaster;
+import org.springframework.context.event.ApplicationListenerMethodAdapter;
 import org.springframework.core.ResolvableType;
 import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.core.env.Environment;
 import org.springframework.lang.NonNull;
+import org.springframework.lang.Nullable;
 import org.springframework.modulith.events.core.EventPublication;
 import org.springframework.modulith.events.core.EventPublicationRegistry;
 import org.springframework.modulith.events.core.PublicationTargetIdentifier;
 import org.springframework.transaction.event.TransactionPhase;
 import org.springframework.transaction.event.TransactionalApplicationListener;
 import org.springframework.transaction.event.TransactionalEventListener;
 import org.springframework.util.Assert;
+import org.springframework.util.ReflectionUtils;
 
 /**
  * An {@link ApplicationEventMulticaster} to register {@link EventPublication}s in an {@link EventPublicationRegistry}
@@ -56,11 +60,17 @@ public class PersistentApplicationEventMulticaster extends AbstractApplicationEv
 		implements SmartInitializingSingleton {
 
 	private static final Logger LOGGER = LoggerFactory.getLogger(PersistentApplicationEventMulticaster.class);
+	private static final Method SUPPORTS_METHOD = ReflectionUtils.findMethod(ApplicationListenerMethodAdapter.class,
+			"shouldHandle", ApplicationEvent.class, Object[].class);
 	static final String REPUBLISH_ON_RESTART = "spring.modulith.republish-outstanding-events-on-restart";
 
 	private final @NonNull Supplier<EventPublicationRegistry> registry;
 	private final @NonNull Supplier<Environment> environment;
 
+	static {
+		ReflectionUtils.makeAccessible(SUPPORTS_METHOD);
+	}
+
 	/**
 	 * Creates a new {@link PersistentApplicationEventMulticaster} for the given {@link EventPublicationRegistry}.
 	 *
@@ -92,7 +102,7 @@ public void multicastEvent(ApplicationEvent event) {
 	 */
 	@Override
 	@SuppressWarnings({ "unchecked", "rawtypes" })
-	public void multicastEvent(ApplicationEvent event, ResolvableType eventType) {
+	public void multicastEvent(ApplicationEvent event, @Nullable ResolvableType eventType) {
 
 		var type = eventType == null ? ResolvableType.forInstance(event) : eventType;
 		var listeners = getApplicationListeners(event, type);
@@ -109,6 +119,22 @@ public void multicastEvent(ApplicationEvent event, ResolvableType eventType) {
 		}
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.context.event.AbstractApplicationEventMulticaster#getApplicationListeners(org.springframework.context.ApplicationEvent, org.springframework.core.ResolvableType)
+	 */
+	@Override
+	protected Collection<ApplicationListener<?>> getApplicationListeners(ApplicationEvent event,
+			ResolvableType eventType) {
+
+		Object eventToPersist = getEventToPersist(event);
+
+		return super.getApplicationListeners(event, eventType)
+				.stream()
+				.filter(it -> matches(event, eventToPersist, it))
+				.toList();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.beans.factory.SmartInitializingSingleton#afterSingletonsInstantiated()
@@ -169,6 +195,18 @@ private static Object getEventToPersist(ApplicationEvent event) {
 				: event;
 	}
 
+	@SuppressWarnings("null")
+	private static boolean matches(ApplicationEvent event, Object payload, ApplicationListener<?> listener) {
+
+		// Verify general listener matching by eagerly evaluating the condition
+		if (!ApplicationListenerMethodAdapter.class.isInstance(listener)) {
+			return true;
+		}
+
+		return (boolean) ReflectionUtils.invokeMethod(SUPPORTS_METHOD, listener, event,
+				new Object[] { payload });
+	}
+
 	/**
 	 * First-class collection to work with transactional event listeners, i.e. {@link ApplicationListener} instances that
 	 * implement {@link TransactionalApplicationListener}.

spring-modulith-events/spring-modulith-events-core/src/test/java/org/springframework/modulith/events/support/PersistentApplicationEventMulticasterUnitTests.java

@@ -15,15 +15,25 @@
  */
 package org.springframework.modulith.events.support;
 
+import static org.assertj.core.api.Assertions.*;
 import static org.mockito.Mockito.*;
 
+import lombok.AllArgsConstructor;
+
 import java.util.Map;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.springframework.context.PayloadApplicationEvent;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.event.ApplicationEventMulticaster;
+import org.springframework.context.event.EventListenerMethodProcessor;
+import org.springframework.core.ResolvableType;
 import org.springframework.core.env.MapPropertySource;
 import org.springframework.core.env.StandardEnvironment;
 import org.springframework.modulith.events.core.EventPublicationRegistry;
+import org.springframework.stereotype.Component;
+import org.springframework.transaction.event.TransactionalEventListener;
 
 /**
  * Unit tests for {@link PersistentApplicationEventMulticaster}.
@@ -61,4 +71,39 @@ void triggersRepublicationIfExplicitlyEnabled() {
 
 		verify(registry).findIncompletePublications();
 	}
+
+	@Test // GH-277
+	void honorsListenerCondition() throws Exception {
+
+		try (var ctx = new AnnotationConfigApplicationContext()) {
+
+			ctx.addBeanFactoryPostProcessor(new EventListenerMethodProcessor());
+			ctx.registerBean("applicationEventMulticaster", ApplicationEventMulticaster.class, () -> multicaster);
+			ctx.registerBean("conditionalListener", ConditionalListener.class);
+			ctx.refresh();
+
+			assertListenerSelected(new SampleEvent(true), true);
+			assertListenerSelected(new SampleEvent(false), false);
+		}
+	}
+
+	private void assertListenerSelected(SampleEvent event, boolean expected) {
+
+		var listeners = multicaster.getApplicationListeners(new PayloadApplicationEvent<>(this, event),
+				ResolvableType.forClass(event.getClass()));
+
+		assertThat(listeners).hasSize(expected ? 1 : 0);
+	}
+
+	@Component
+	static class ConditionalListener {
+
+		@TransactionalEventListener(condition = "#event.supported")
+		void on(SampleEvent event) {}
+	}
+
+	@AllArgsConstructor
+	static class SampleEvent {
+		public boolean supported;
+	}
 }