Merge pull request #16104 from ayudovin

* pr/16104:
  Polish "Add default no-op method to SpringApplicationRunListener"
  Add default no-op method to SpringApplicationRunListener

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplicationRunListener.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -38,28 +38,32 @@ public interface SpringApplicationRunListener {
 	 * Called immediately when the run method has first started. Can be used for very
 	 * early initialization.
 	 */
-	void starting();
+	default void starting() {
+	}
 
 	/**
 	 * Called once the environment has been prepared, but before the
 	 * {@link ApplicationContext} has been created.
 	 * @param environment the environment
 	 */
-	void environmentPrepared(ConfigurableEnvironment environment);
+	default void environmentPrepared(ConfigurableEnvironment environment) {
+	}
 
 	/**
 	 * Called once the {@link ApplicationContext} has been created and prepared, but
 	 * before sources have been loaded.
 	 * @param context the application context
 	 */
-	void contextPrepared(ConfigurableApplicationContext context);
+	default void contextPrepared(ConfigurableApplicationContext context) {
+	}
 
 	/**
 	 * Called once the application context has been loaded but before it has been
 	 * refreshed.
 	 * @param context the application context
 	 */
-	void contextLoaded(ConfigurableApplicationContext context);
+	default void contextLoaded(ConfigurableApplicationContext context) {
+	}
 
 	/**
 	 * The context has been refreshed and the application has started but
@@ -68,7 +72,8 @@ public interface SpringApplicationRunListener {
 	 * @param context the application context.
 	 * @since 2.0.0
 	 */
-	void started(ConfigurableApplicationContext context);
+	default void started(ConfigurableApplicationContext context) {
+	}
 
 	/**
 	 * Called immediately before the run method finishes, when the application context has
@@ -77,7 +82,8 @@ public interface SpringApplicationRunListener {
 	 * @param context the application context.
 	 * @since 2.0.0
 	 */
-	void running(ConfigurableApplicationContext context);
+	default void running(ConfigurableApplicationContext context) {
+	}
 
 	/**
 	 * Called when a failure occurs when running the application.
@@ -86,6 +92,7 @@ public interface SpringApplicationRunListener {
 	 * @param exception the failure
 	 * @since 2.0.0
 	 */
-	void failed(ConfigurableApplicationContext context, Throwable exception);
+	default void failed(ConfigurableApplicationContext context, Throwable exception) {
+	}
 
 }