Add ResolvableTypeProvider

Provide a mean to detect the actual ResolvableType based on a instance as
a counter measure to type erasure.

Upgrade the event infrastructure to detect if the event (or the payload)
implements such interface. When this is the case, the return value of
`getResolvableType` is used to validate its generic type against the
method signature of the listener.

Issue: SPR-13069

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

@@ -21,6 +21,7 @@ import java.io.IOException;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationListener;
 import org.springframework.core.ResolvableType;
+import org.springframework.core.ResolvableTypeProvider;
 
 /**
  * @author Stephane Nicoll
@@ -53,6 +54,23 @@ public abstract class AbstractApplicationEventListenerTests {
 
 	}
 
+	protected static class SmartGenericTestEvent<T>
+			extends GenericTestEvent<T> implements ResolvableTypeProvider {
+
+		private final ResolvableType resolvableType;
+
+		public SmartGenericTestEvent(Object source, T payload) {
+			super(source, payload);
+			this.resolvableType = ResolvableType.forClassWithGenerics(
+					getClass(), payload.getClass());
+		}
+
+		@Override
+		public ResolvableType getResolvableType() {
+			return this.resolvableType;
+		}
+	}
+
 	protected static class StringEvent extends GenericTestEvent<String> {
 
 		public StringEvent(Object source, String payload) {

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

@@ -75,7 +75,7 @@ public class ApplicationContextEventTests extends AbstractApplicationEventListen
 				getGenericApplicationEventType("longEvent"));
 	}
 
-	@Test // Unfortunate - this should work as well
+	@Test
 	public void multicastGenericEventWildcardSubType() {
 		multicastEvent(false, StringEventListener.class, createGenericTestEvent("test"),
 				getGenericApplicationEventType("wildcardEvent"));
@@ -91,6 +91,16 @@ public class ApplicationContextEventTests extends AbstractApplicationEventListen
 		multicastEvent(false, StringEventListener.class, new LongEvent(this, 123L), null);
 	}
 
+	@Test
+	public void multicastSmartGenericTypeGenericListener() {
+		multicastEvent(true, StringEventListener.class, new SmartGenericTestEvent<>(this, "test"), null);
+	}
+
+	@Test
+	public void multicastSmartGenericWrongTypeGenericListener() {
+		multicastEvent(false, StringEventListener.class, new SmartGenericTestEvent<>(this, 123L), null);
+	}
+
 	private void multicastEvent(boolean match, Class<?> listenerType,
 			ApplicationEvent event, ResolvableType eventType) {
 		@SuppressWarnings("unchecked")

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

@@ -29,6 +29,7 @@ import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.PayloadApplicationEvent;
 import org.springframework.core.ResolvableType;
+import org.springframework.core.ResolvableTypeProvider;
 import org.springframework.core.annotation.Order;
 import org.springframework.util.ReflectionUtils;
 
@@ -155,6 +156,42 @@ public class ApplicationListenerMethodAdapterTests extends AbstractApplicationEv
 		verify(this.sampleEvents, times(1)).handleGenericString(event);
 	}
 
+	@Test
+	public void invokeListenerWithGenericEvent() {
+		Method method = ReflectionUtils.findMethod(SampleEvents.class,
+				"handleGenericString", GenericTestEvent.class);
+		GenericTestEvent<String> event = new SmartGenericTestEvent<>(this, "test");
+		invokeListener(method, event);
+		verify(this.sampleEvents, times(1)).handleGenericString(event);
+	}
+
+	@Test
+	public void invokeListenerWithGenericPayload() {
+		Method method = ReflectionUtils.findMethod(SampleEvents.class,
+				"handleGenericStringPayload", EntityWrapper.class);
+		EntityWrapper<String> payload = new EntityWrapper<>("test");
+		invokeListener(method, new PayloadApplicationEvent<>(this, payload));
+		verify(this.sampleEvents, times(1)).handleGenericStringPayload(payload);
+	}
+
+	@Test
+	public void invokeListenerWithWrongGenericPayload() {
+		Method method = ReflectionUtils.findMethod(SampleEvents.class,
+				"handleGenericStringPayload", EntityWrapper.class);
+		EntityWrapper<Integer> payload = new EntityWrapper<>(123);
+		invokeListener(method, new PayloadApplicationEvent<>(this, payload));
+		verify(this.sampleEvents, times(0)).handleGenericStringPayload(any());
+	}
+
+	@Test
+	public void invokeListenerWithAnyGenericPayload() {
+		Method method = ReflectionUtils.findMethod(SampleEvents.class,
+				"handleGenericAnyPayload", EntityWrapper.class);
+		EntityWrapper<String> payload = new EntityWrapper<>("test");
+		invokeListener(method, new PayloadApplicationEvent<>(this, payload));
+		verify(this.sampleEvents, times(1)).handleGenericAnyPayload(payload);
+	}
+
 	@Test
 	public void invokeListenerRuntimeException() {
 		Method method = ReflectionUtils.findMethod(SampleEvents.class,
@@ -284,6 +321,16 @@ public class ApplicationListenerMethodAdapterTests extends AbstractApplicationEv
 		public void handleString(String payload) {
 		}
 
+		@EventListener
+		public void handleGenericStringPayload(EntityWrapper<String> event) {
+
+		}
+
+		@EventListener
+		public void handleGenericAnyPayload(EntityWrapper<?> event) {
+
+		}
+
 		@EventListener
 		public void tooManyParameters(String event, String whatIsThis) {
 		}
@@ -313,6 +360,19 @@ public class ApplicationListenerMethodAdapterTests extends AbstractApplicationEv
 
 	}
 
+	private static class EntityWrapper<T> implements ResolvableTypeProvider {
+		private final T entity;
+
+		public EntityWrapper(T entity) {
+			this.entity = entity;
+		}
+
+		@Override
+		public ResolvableType getResolvableType() {
+			return ResolvableType.forClassWithGenerics(getClass(), this.entity.getClass());
+		}
+	}
+
 	static class InvalidProxyTestBean implements SimpleService {
 
 		@Override

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

@@ -66,6 +66,12 @@ public class GenericApplicationListenerAdapterTests extends AbstractApplicationE
 		supportsEventType(true, StringEventListener.class, eventType);
 	}
 
+	@Test // or if the event provides its precise type
+	public void genericListenerStrictTypeAndResolvableTypeProvider() {
+		ResolvableType eventType = new SmartGenericTestEvent<>(this, "foo").getResolvableType();
+		supportsEventType(true, StringEventListener.class, eventType);
+	}
+
 	@Test // Demonstrates it works if we actually use the subtype
 	public void genericListenerStrictTypeEventSubType() {
 		StringEvent stringEvent = new StringEvent(this, "test");