Merge pull request #24599 from chenqimiao

* pr/24599:
  Polish "Add support for explicit generic type in PayloadApplicationEvent"
  Add support for explicit generic type in PayloadApplicationEvent

Closes 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)
@@ -37,22 +39,34 @@ public class PayloadApplicationEvent<T> extends ApplicationEvent implements Reso
 
 	private final T payload;
 
+	private final ResolvableType payloadType;
 
 	/**
 	 * 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) {
+	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 != null) ? payloadType : ResolvableType.forInstance(payload);
+	}
+
+	/**
+	 * Create a new PayloadApplicationEvent, using the instance to infer its type.
+	 * @param source the object on which the event initially occurred (never {@code null})
+	 * @param payload the payload object (never {@code null})
+	 */
+	public PayloadApplicationEvent(Object source, T payload) {
+		this(source, payload, null);
 	}
 
 
 	@Override
 	public ResolvableType getResolvableType() {
-		return ResolvableType.forClassWithGenerics(getClass(), 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/PayloadApplicationEventTests.java

@@ -27,6 +27,7 @@ import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.PayloadApplicationEvent;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.core.ResolvableType;
 import org.springframework.stereotype.Component;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -34,10 +35,40 @@ import static org.assertj.core.api.Assertions.assertThat;
 /**
  * @author Juergen Hoeller
  */
-public class PayloadApplicationEventTests {
+class PayloadApplicationEventTests {
 
 	@Test
-	public void testEventClassWithInterface() {
+	void payloadApplicationEventWithNoTypeUsesInstance() {
+		NumberHolder<Integer> payload = new NumberHolder<>(42);
+		PayloadApplicationEvent<NumberHolder<Integer>> event = new PayloadApplicationEvent<>(this, payload);
+		assertThat(event.getResolvableType()).satisfies(eventType -> {
+			assertThat(eventType.toClass()).isEqualTo(PayloadApplicationEvent.class);
+			assertThat(eventType.getGenerics()).hasSize(1);
+			assertThat(eventType.getGenerics()[0]).satisfies(bodyType -> {
+				assertThat(bodyType.toClass()).isEqualTo(NumberHolder.class);
+				assertThat(bodyType.hasUnresolvableGenerics()).isTrue();
+			});
+		});
+	}
+
+	@Test
+	void payloadApplicationEventWithType() {
+		NumberHolder<Integer> payload = new NumberHolder<>(42);
+		ResolvableType payloadType = ResolvableType.forClassWithGenerics(NumberHolder.class, Integer.class);
+		PayloadApplicationEvent<NumberHolder<Integer>> event = new PayloadApplicationEvent<>(this, payload, payloadType);
+		assertThat(event.getResolvableType()).satisfies(eventType -> {
+			assertThat(eventType.toClass()).isEqualTo(PayloadApplicationEvent.class);
+			assertThat(eventType.getGenerics()).hasSize(1);
+			assertThat(eventType.getGenerics()[0]).satisfies(bodyType -> {
+				assertThat(bodyType.toClass()).isEqualTo(NumberHolder.class);
+				assertThat(bodyType.hasUnresolvableGenerics()).isFalse();
+				assertThat(bodyType.getGenerics()[0].toClass()).isEqualTo(Integer.class);
+			});
+		});
+	}
+
+	@Test
+	void testEventClassWithInterface() {
 		ApplicationContext ac = new AnnotationConfigApplicationContext(AuditableListener.class);
 
 		AuditablePayloadEvent<String> event = new AuditablePayloadEvent<>(this, "xyz");
@@ -46,7 +77,7 @@ public class PayloadApplicationEventTests {
 	}
 
 	@Test
-	public void testProgrammaticEventListener() {
+	void testProgrammaticEventListener() {
 		List<Auditable> events = new ArrayList<>();
 		ApplicationListener<AuditablePayloadEvent<String>> listener = events::add;
 		ApplicationListener<AuditablePayloadEvent<Integer>> mismatch = (event -> event.getPayload().intValue());
@@ -62,7 +93,7 @@ public class PayloadApplicationEventTests {
 	}
 
 	@Test
-	public void testProgrammaticPayloadListener() {
+	void testProgrammaticPayloadListener() {
 		List<String> events = new ArrayList<>();
 		ApplicationListener<PayloadApplicationEvent<String>> listener = ApplicationListener.forPayload(events::add);
 		ApplicationListener<PayloadApplicationEvent<Integer>> mismatch = ApplicationListener.forPayload(payload -> payload.intValue());
@@ -102,4 +133,14 @@ public class PayloadApplicationEventTests {
 		}
 	}
 
+	static class NumberHolder<T extends Number> {
+
+		private T number;
+
+		public NumberHolder(T number) {
+			this.number = number;
+		}
+
+	}
+
 }