Support for Collection-based return type

If an `@EventListener` annotated method returns a Collection or an Array,
each individual items are now published as an event instead of publishing
one event with said collection.

Issue: SPR-12733

Author: snicoll

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

@@ -19,8 +19,8 @@
 import java.lang.annotation.Annotation;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
-import java.lang.reflect.Parameter;
 import java.lang.reflect.UndeclaredThrowableException;
+import java.util.Collection;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -37,6 +37,7 @@
 import org.springframework.core.annotation.Order;
 import org.springframework.expression.EvaluationContext;
 import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
 import org.springframework.util.ReflectionUtils;
 import org.springframework.util.StringUtils;
 
@@ -136,7 +137,27 @@ protected Object[] resolveArguments(ApplicationEvent event) {
 
 	protected void handleResult(Object result) {
 		Assert.notNull(this.applicationContext, "ApplicationContext must no be null.");
-		this.applicationContext.publishEvent(result);
+		if (result.getClass().isArray()) {
+			Object[] events = ObjectUtils.toObjectArray(result);
+			for (Object event : events) {
+				publishEvent(event);
+			}
+		}
+		else if (result instanceof Collection<?>) {
+			Collection<?> events = (Collection<?>) result;
+			for (Object event : events) {
+				publishEvent(event);
+			}
+		}
+		else {
+			publishEvent(result);
+		}
+	}
+
+	private void publishEvent(Object event) {
+		if (event != null) {
+			this.applicationContext.publishEvent(event);
+		}
 	}
 
 

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

@@ -22,7 +22,9 @@
 import java.lang.annotation.Target;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Set;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 
@@ -157,7 +159,7 @@ public void simpleReply() {
 		this.eventCollector.assertNoEventReceived(replyEventListener);
 		this.context.publishEvent(event);
 		this.eventCollector.assertEvent(replyEventListener, event);
-		this.eventCollector.assertEvent(listener, new TestEvent(replyEventListener, event.getId(), event.msg)); // reply
+		this.eventCollector.assertEvent(listener, new TestEvent(replyEventListener, event.getId(), "dummy")); // reply
 		this.eventCollector.assertTotalEventsCount(2);
 	}
 
@@ -176,6 +178,55 @@ public void nullReplyIgnored() {
 		this.eventCollector.assertTotalEventsCount(1);
 	}
 
+	@Test
+	public void arrayReply() {
+		load(TestEventListener.class, ReplyEventListener.class);
+		AnotherTestEvent event = new AnotherTestEvent(this, new String[]{"first", "second"});
+		ReplyEventListener replyEventListener = this.context.getBean(ReplyEventListener.class);
+		TestEventListener listener = this.context.getBean(TestEventListener.class);
+
+		this.eventCollector.assertNoEventReceived(listener);
+		this.eventCollector.assertNoEventReceived(replyEventListener);
+		this.context.publishEvent(event);
+		this.eventCollector.assertEvent(replyEventListener, event);
+		this.eventCollector.assertEvent(listener, "first", "second"); // reply
+		this.eventCollector.assertTotalEventsCount(3);
+	}
+
+	@Test
+	public void collectionReply() {
+		load(TestEventListener.class, ReplyEventListener.class);
+		Set<Object> replies = new LinkedHashSet<>();
+		replies.add("first");
+		replies.add(4L);
+		replies.add("third");
+		AnotherTestEvent event = new AnotherTestEvent(this, replies);
+		ReplyEventListener replyEventListener = this.context.getBean(ReplyEventListener.class);
+		TestEventListener listener = this.context.getBean(TestEventListener.class);
+
+		this.eventCollector.assertNoEventReceived(listener);
+		this.eventCollector.assertNoEventReceived(replyEventListener);
+		this.context.publishEvent(event);
+		this.eventCollector.assertEvent(replyEventListener, event);
+		this.eventCollector.assertEvent(listener, "first", "third"); // reply (no listener for 4L)
+		this.eventCollector.assertTotalEventsCount(3);
+	}
+
+	@Test
+	public void collectionReplyNullValue() {
+		load(TestEventListener.class, ReplyEventListener.class);
+		AnotherTestEvent event = new AnotherTestEvent(this, Arrays.asList(null, "test"));
+		ReplyEventListener replyEventListener = this.context.getBean(ReplyEventListener.class);
+		TestEventListener listener = this.context.getBean(TestEventListener.class);
+
+		this.eventCollector.assertNoEventReceived(listener);
+		this.eventCollector.assertNoEventReceived(replyEventListener);
+		this.context.publishEvent(event);
+		this.eventCollector.assertEvent(replyEventListener, event);
+		this.eventCollector.assertEvent(listener, "test");
+		this.eventCollector.assertTotalEventsCount(2);
+	}
+
 	@Test
 	public void eventListenerWorksWithInterfaceProxy() throws Exception {
 		load(ProxyTestBean.class);
@@ -464,15 +515,19 @@ static class ReplyEventListener extends AbstractTestEventListener {
 		@EventListener
 		public Object handle(AnotherTestEvent event) {
 			collectEvent(event);
-			if (event.msg == null) {
+			if (event.content == null) {
 				return null;
 			}
-			else if (event.msg.equals("String")) {
-				return event.msg;
-			}
-			else {
-				return new TestEvent(this, event.getId(), event.msg);
+			else if (event.content instanceof String) {
+				String s = (String) event.content;
+				if (s.equals("String")) {
+					return event.content;
+				}
+				else {
+					return new TestEvent(this, event.getId(), s);
+				}
 			}
+			return event.content;
 		}
 
 	}
@@ -495,7 +550,7 @@ public void handle(TestEvent event) {
 		@Async
 		public void handleAsync(AnotherTestEvent event) {
 			collectEvent(event);
-			if ("fail".equals(event.msg)) {
+			if ("fail".equals(event.content)) {
 				countDownLatch.countDown();
 				throw new IllegalStateException("Test exception");
 			}
@@ -517,7 +572,7 @@ static class AsyncEventListener extends AbstractTestEventListener {
 		@EventListener
 		@Async
 		public void handleAsync(AnotherTestEvent event) {
-			assertTrue(!Thread.currentThread().getName().equals(event.msg));
+			assertTrue(!Thread.currentThread().getName().equals(event.content));
 			collectEvent(event);
 			countDownLatch.countDown();
 		}

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

@@ -22,11 +22,11 @@
 @SuppressWarnings("serial")
 public class AnotherTestEvent extends IdentifiableApplicationEvent {
 
-	public final String msg;
+	public final Object content;
 
-	public AnotherTestEvent(Object source, String msg) {
+	public AnotherTestEvent(Object source, Object content) {
 		super(source);
-		this.msg = msg;
+		this.content = content;
 	}
 
 }