Introduce TransactionalApplicationListener interface (with callback support)

Includes forPayload methods and common adapter classes for programmatic usage.
Aligns default order values for event handling delegates to LOWEST_PRECEDENCE.

Closes gh-24163

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

@@ -26,6 +26,7 @@ import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.PayloadApplicationEvent;
+import org.springframework.core.Ordered;
 import org.springframework.core.ResolvableType;
 import org.springframework.core.ResolvableTypeProvider;
 import org.springframework.core.annotation.Order;
@@ -161,7 +162,7 @@ public class ApplicationListenerMethodAdapterTests extends AbstractApplicationEv
 		Method method = ReflectionUtils.findMethod(
 				SampleEvents.class, "handleGenericString", GenericTestEvent.class);
 		ApplicationListenerMethodAdapter adapter = createTestInstance(method);
-		assertThat(adapter.getOrder()).isEqualTo(0);
+		assertThat(adapter.getOrder()).isEqualTo(Ordered.LOWEST_PRECEDENCE);
 	}
 
 	@Test

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -22,8 +22,11 @@ import java.util.List;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.context.ApplicationContext;
+import org.springframework.context.ApplicationListener;
+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.stereotype.Component;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -34,14 +37,42 @@ import static org.assertj.core.api.Assertions.assertThat;
 public class PayloadApplicationEventTests {
 
 	@Test
-	@SuppressWarnings({ "rawtypes", "resource" })
 	public void testEventClassWithInterface() {
 		ApplicationContext ac = new AnnotationConfigApplicationContext(AuditableListener.class);
-		AuditablePayloadEvent event = new AuditablePayloadEvent<>(this, "xyz");
+
+		AuditablePayloadEvent<String> event = new AuditablePayloadEvent<>(this, "xyz");
 		ac.publishEvent(event);
 		assertThat(ac.getBean(AuditableListener.class).events.contains(event)).isTrue();
 	}
 
+	@Test
+	public void testProgrammaticEventListener() {
+		List<Auditable> events = new ArrayList<>();
+		ApplicationListener<AuditablePayloadEvent<String>> listener = events::add;
+
+		ConfigurableApplicationContext ac = new GenericApplicationContext();
+		ac.addApplicationListener(listener);
+		ac.refresh();
+
+		AuditablePayloadEvent<String> event = new AuditablePayloadEvent<>(this, "xyz");
+		ac.publishEvent(event);
+		assertThat(events.contains(event)).isTrue();
+	}
+
+	@Test
+	public void testProgrammaticPayloadListener() {
+		List<String> events = new ArrayList<>();
+		ApplicationListener<PayloadApplicationEvent<String>> listener = ApplicationListener.forPayload(events::add);
+
+		ConfigurableApplicationContext ac = new GenericApplicationContext();
+		ac.addApplicationListener(listener);
+		ac.refresh();
+
+		AuditablePayloadEvent<String> event = new AuditablePayloadEvent<>(this, "xyz");
+		ac.publishEvent(event);
+		assertThat(events.contains(event.getPayload())).isTrue();
+	}
+
 
 	public interface Auditable {
 	}