Avoid duplicate ApplicationListener firing (proxy vs. target)

spring-context/src/main/java/org/springframework/context/event/AbstractApplicationEventMulticaster.java

@@ -262,6 +262,24 @@ private Collection<ApplicationListener<?>> retrieveApplicationListeners(
 					if (supportsEvent(beanFactory, listenerBeanName, eventType)) {
 						ApplicationListener<?> listener =
 								beanFactory.getBean(listenerBeanName, ApplicationListener.class);
+
+						// Despite best efforts to avoid it, unwrapped proxies (singleton targets) can end up in the
+						// list of programmatically registered listeners. In order to avoid duplicates, we need to find
+						// and replace them by their proxy counterparts, because if both a proxy and its target end up
+						// in 'allListeners', listeners will fire twice.
+						ApplicationListener<?> unwrappedListener =
+								(ApplicationListener<?>) AopProxyUtils.getSingletonTarget(listener);
+						if (listener != unwrappedListener) {
+							if (filteredListeners != null && filteredListeners.contains(unwrappedListener)) {
+								filteredListeners.remove(unwrappedListener);
+								filteredListeners.add(listener);
+							}
+							if (allListeners.contains(unwrappedListener)) {
+								allListeners.remove(unwrappedListener);
+								allListeners.add(listener);
+							}
+						}
+
 						if (!allListeners.contains(listener) && supportsEvent(listener, eventType, sourceType)) {
 							if (retriever != null) {
 								if (beanFactory.isSingleton(listenerBeanName)) {

spring-context/src/test/java/org/springframework/context/event/ApplicationContextEventTests.java

@@ -39,6 +39,11 @@
 import org.springframework.context.ApplicationEventPublisherAware;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.PayloadApplicationEvent;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.event.test.self_inject.MyApplication;
+import org.springframework.context.event.test.self_inject.MyEventListener;
+import org.springframework.context.event.test.self_inject.MyEventPublisher;
+import org.springframework.context.support.AbstractApplicationContext;
 import org.springframework.context.support.GenericApplicationContext;
 import org.springframework.context.support.StaticApplicationContext;
 import org.springframework.context.support.StaticMessageSource;
@@ -244,6 +249,24 @@ public void proxiedListenersMixedWithTargetListeners() {
 		assertThat(listener1.seenEvents).hasSize(2);
 	}
 
+	/**
+	 * Regression test for <a href="https://github.com/spring-projects/spring-framework/issues/28283">issue 28283</a>,
+	 * where event listeners proxied due to e.g.
+	 * <ul>
+	 *   <li>{@code @Transactional} annotations in their methods or</li>
+	 *   <li>being targeted by aspects</li>
+	 * </ul>
+	 * were added to the list of application listener beans twice (both proxy and unwrapped target).
+	 */
+	@Test
+	public void eventForSelfInjectedProxiedListenerFiredOnlyOnce() {
+		String basePackage = MyApplication.class.getPackageName();
+		AbstractApplicationContext context = new AnnotationConfigApplicationContext(basePackage);
+		context.getBean(MyEventPublisher.class).publishMyEvent("hello");
+		assertThat(MyEventListener.eventCount).isEqualTo(1);
+		context.close();
+	}
+
 	@Test
 	public void testEventPublicationInterceptor() throws Throwable {
 		MethodInvocation invocation = mock();

spring-context/src/test/java/org/springframework/context/event/test/self_inject/MyApplication.java

@@ -0,0 +1,17 @@
+package org.springframework.context.event.test.self_inject;
+
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.EnableAspectJAutoProxy;
+import org.springframework.context.support.AbstractApplicationContext;
+
+@Configuration
+@EnableAspectJAutoProxy(proxyTargetClass = true)
+public class MyApplication {
+	public static void main(String[] args) {
+		try (AbstractApplicationContext context = new AnnotationConfigApplicationContext("org.springframework.context.event.test.self_inject")) {
+			context.getBean(MyEventPublisher.class).publishMyEvent("hello");
+			assert MyEventListener.eventCount == 1 : "event listener must fire exactly once";
+		}
+	}
+}

spring-context/src/test/java/org/springframework/context/event/test/self_inject/MyAspect.java

@@ -0,0 +1,15 @@
+package org.springframework.context.event.test.self_inject;
+
+import org.aspectj.lang.JoinPoint;
+import org.aspectj.lang.annotation.Aspect;
+import org.aspectj.lang.annotation.Before;
+import org.springframework.stereotype.Component;
+
+@Aspect
+@Component
+public class MyAspect {
+	@Before("within(org.springframework.context.event.test.self_inject.MyEventListener)")
+	public void myAdvice(JoinPoint joinPoint) {
+		//System.out.println(joinPoint);
+	}
+}

spring-context/src/test/java/org/springframework/context/event/test/self_inject/MyEvent.java

@@ -0,0 +1,12 @@
+package org.springframework.context.event.test.self_inject;
+
+import org.springframework.context.ApplicationEvent;
+
+public class MyEvent extends ApplicationEvent {
+	private String message;
+
+	public MyEvent(Object source, String message) {
+		super(source);
+		this.message = message;
+	}
+}

spring-context/src/test/java/org/springframework/context/event/test/self_inject/MyEventListener.java

@@ -0,0 +1,20 @@
+package org.springframework.context.event.test.self_inject;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.ApplicationListener;
+import org.springframework.stereotype.Component;
+
+@Component
+public class MyEventListener implements ApplicationListener<MyEvent> {
+	public static int eventCount;
+
+	@Autowired  // use '-Dspring.main.allow-circular-references=true' in Spring Boot >= 2.6.0
+	//@Lazy     // with '@Lazy', the problem does not occur
+	private MyEventListener eventDemoListener;
+
+	@Override
+	public void onApplicationEvent(MyEvent event) {
+		//System.out.println("Event: " + event);
+		eventCount++;
+	}
+}

spring-context/src/test/java/org/springframework/context/event/test/self_inject/MyEventPublisher.java

@@ -0,0 +1,15 @@
+package org.springframework.context.event.test.self_inject;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.stereotype.Component;
+
+@Component
+public class MyEventPublisher {
+	@Autowired
+	private ApplicationEventPublisher eventPublisher;
+
+	public void publishMyEvent(String message) {
+		eventPublisher.publishEvent(new MyEvent(this, message));
+	}
+}