Add support for functional registration of application listener

This commit adds a functional style registration of an application
listener for a particular event. Rather than introducing another method
at the ConfigurableApplicationContext interface level, this commit
provides a factory method in GenericApplicationListener.

Closes gh-21411

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,8 @@
 
 package org.springframework.context.event;
 
+import java.util.function.Consumer;
+
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationListener;
 import org.springframework.core.ResolvableType;
@@ -53,4 +55,16 @@ public interface GenericApplicationListener extends SmartApplicationListener {
 	 */
 	boolean supportsEventType(ResolvableType eventType);
 
+	/**
+	 * Create a new {@code ApplicationListener} for the given event type.
+	 * @param eventType the event to listen to
+	 * @param consumer the consumer to invoke when a matching event is fired
+	 * @param <E> the specific {@code ApplicationEvent} subclass to listen to
+	 * @return a corresponding {@code ApplicationListener} instance
+	 * @since 6.1.3
+	 */
+	static <E extends ApplicationEvent> GenericApplicationListener forEventType(Class<E> eventType, Consumer<E> consumer) {
+		return new GenericApplicationListenerDelegate<>(eventType, consumer);
+	}
+
 }

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

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2002-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.context.event;
+
+import java.util.function.Consumer;
+
+import org.springframework.context.ApplicationEvent;
+import org.springframework.core.ResolvableType;
+
+/**
+ * A {@link GenericApplicationListener} implementation that supports a single
+ * event type.
+ *
+ * @author Stephane Nicoll
+ * @since 6.1.3
+ * @param <E> the specific {@code ApplicationEvent} subclass to listen to
+ */
+class GenericApplicationListenerDelegate<E extends ApplicationEvent> implements GenericApplicationListener {
+
+	private final Class<E> supportedEventType;
+
+	private final Consumer<E> consumer;
+
+	GenericApplicationListenerDelegate(Class<E> supportedEventType, Consumer<E> consumer) {
+		this.supportedEventType = supportedEventType;
+		this.consumer = consumer;
+	}
+
+	@Override
+	public void onApplicationEvent(ApplicationEvent event) {
+		this.consumer.accept(this.supportedEventType.cast(event));
+	}
+
+	@Override
+	public boolean supportsEventType(ResolvableType eventType) {
+		return this.supportedEventType.isAssignableFrom(eventType.toClass());
+	}
+
+}