Add support for explicit generic type in PayloadApplicationEvent

See gh-24599

spring-context/src/main/java/org/springframework/context/PayloadApplicationEvent.java

@@ -20,6 +20,7 @@ import java.util.function.Consumer;
 
 import org.springframework.core.ResolvableType;
 import org.springframework.core.ResolvableTypeProvider;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -27,6 +28,7 @@ import org.springframework.util.Assert;
  *
  * @author Stephane Nicoll
  * @author Juergen Hoeller
+ * @author Qimiao Chen
  * @since 4.2
  * @param <T> the payload type of the event
  * @see ApplicationEventPublisher#publishEvent(Object)
@@ -37,6 +39,8 @@ public class PayloadApplicationEvent<T> extends ApplicationEvent implements Reso
 
 	private final T payload;
 
+	@Nullable
+	private ResolvableType payloadType;
 
 	/**
 	 * Create a new PayloadApplicationEvent.
@@ -44,15 +48,29 @@ public class PayloadApplicationEvent<T> extends ApplicationEvent implements Reso
 	 * @param payload the payload object (never {@code null})
 	 */
 	public PayloadApplicationEvent(Object source, T payload) {
+		this(source, payload, null);
+	}
+
+	/**
+	 * Create a new PayloadApplicationEvent.
+	 * @param source the object on which the event initially occurred (never {@code null})
+	 * @param payload the payload object (never {@code null})
+	 * @param payloadType the type object of payload object (can be {@code null})
+	 */
+	public PayloadApplicationEvent(Object source, T payload, @Nullable ResolvableType payloadType) {
 		super(source);
 		Assert.notNull(payload, "Payload must not be null");
 		this.payload = payload;
+		this.payloadType = payloadType;
 	}
 
 
 	@Override
 	public ResolvableType getResolvableType() {
-		return ResolvableType.forClassWithGenerics(getClass(), ResolvableType.forInstance(getPayload()));
+		if (this.payloadType == null) {
+			this.payloadType = ResolvableType.forInstance(getPayload());
+		}
+		return ResolvableType.forClassWithGenerics(getClass(), this.payloadType);
 	}
 
 	/**

spring-context/src/main/java/org/springframework/context/support/AbstractApplicationContext.java

@@ -407,7 +407,7 @@ public abstract class AbstractApplicationContext extends DefaultResourceLoader
 			applicationEvent = (ApplicationEvent) event;
 		}
 		else {
-			applicationEvent = new PayloadApplicationEvent<>(this, event);
+			applicationEvent = new PayloadApplicationEvent<>(this, event, eventType);
 			if (eventType == null) {
 				eventType = ((PayloadApplicationEvent<?>) applicationEvent).getResolvableType();
 			}

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

@@ -60,6 +60,7 @@ import org.springframework.context.event.test.GenericEventPojo;
 import org.springframework.context.event.test.Identifiable;
 import org.springframework.context.event.test.TestEvent;
 import org.springframework.context.support.ClassPathXmlApplicationContext;
+import org.springframework.core.ResolvableType;
 import org.springframework.core.annotation.AliasFor;
 import org.springframework.core.annotation.Order;
 import org.springframework.scheduling.annotation.Async;
@@ -622,6 +623,17 @@ class AnnotationDrivenEventListenerTests {
 		this.eventCollector.assertNoEventReceived(listener);
 		this.eventCollector.assertTotalEventsCount(0);
 	}
+	@Test
+	public void publishEventWithGeneric() throws NoSuchMethodException {
+		MyAnnotationConfigApplicationContext ctx = new MyAnnotationConfigApplicationContext();
+		context = ctx;
+		ctx.register(MyEventWithGenericListener.class);
+		ctx.refresh();
+		ResolvableType resolvableType = ResolvableType.forMethodParameter(MyEventWithGenericListener.class.getMethod("onMyEventWithGeneric",MyEventWithGeneric.class),0);
+		ctx.publishEvent(new MyEventWithGeneric<String>(),resolvableType);
+		assertThat(MyEventWithGenericListener.count).isEqualTo(1);
+	}
+
 
 	@Test
 	void orderedListeners() {
@@ -1134,4 +1146,29 @@ class AnnotationDrivenEventListenerTests {
 		}
 	}
 
+	public static class MyAnnotationConfigApplicationContext extends AnnotationConfigApplicationContext{
+
+		@Override
+		public void publishEvent(Object event, ResolvableType eventType) {
+			super.publishEvent(event, eventType);
+		}
+	}
+
+	public static class MyEventWithGeneric<T> {
+
+	}
+
+	@Component
+	public static class MyEventWithGenericListener{
+
+		public static int count ;
+
+		@EventListener
+		public void onMyEventWithGeneric(MyEventWithGeneric<String> event){
+			count ++;
+		}
+
+
+	}
+
 }