Improve documentation for the default profile

Closes gh-29071

Author: snicoll

framework-docs/modules/ROOT/pages/core/beans/environment.adoc

@@ -562,8 +562,9 @@ If no profile is active, the `dataSource` is created. You can see this
 as a way to provide a default definition for one or more beans. If any
 profile is enabled, the default profile does not apply.
 
-You can change the name of the default profile by using `setDefaultProfiles()` on
-the `Environment` or, declaratively, by using the `spring.profiles.default` property.
+The name of the default profile is `default`. You can change the name of
+the default profile by using `setDefaultProfiles()` on the `Environment` or,
+declaratively, by using the `spring.profiles.default` property.
 
 
 

spring-context/src/main/java/org/springframework/context/annotation/Profile.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -38,6 +38,14 @@
  * for web applications. Profiles may also be activated declaratively in
  * integration tests via the {@code @ActiveProfiles} annotation.
  *
+ * <p>If no profile is active using one of those options, a default profile is
+ * enabled as a fallback. The name of the default profile is
+ * {@value AbstractEnvironment#RESERVED_DEFAULT_PROFILE_NAME}. This can be changed
+ * via {@link ConfigurableEnvironment#setDefaultProfiles} or declaratively by
+ * setting the {@link AbstractEnvironment#DEFAULT_PROFILES_PROPERTY_NAME
+ * spring.profiles.default} property as a JVM system property, as an environment
+ * variable, or as a Servlet context parameter in {@code web.xml} for web applications.
+ *
  * <p>The {@code @Profile} annotation may be used in any of the following ways:
  * <ul>
  * <li>as a type-level annotation on any class directly or indirectly annotated with

spring-core/src/main/java/org/springframework/core/env/AbstractEnvironment.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -89,15 +89,15 @@ public abstract class AbstractEnvironment implements ConfigurableEnvironment {
 
 	/**
 	 * Name of reserved default profile name: {@value}. If no default profile names are
-	 * explicitly and no active profile names are explicitly set, this profile will
+	 * explicitly set and no active profile names are explicitly set, this profile will
 	 * automatically be activated by default.
 	 * @see #getReservedDefaultProfiles
 	 * @see ConfigurableEnvironment#setDefaultProfiles
 	 * @see ConfigurableEnvironment#setActiveProfiles
 	 * @see AbstractEnvironment#DEFAULT_PROFILES_PROPERTY_NAME
 	 * @see AbstractEnvironment#ACTIVE_PROFILES_PROPERTY_NAME
 	 */
-	protected static final String RESERVED_DEFAULT_PROFILE_NAME = "default";
+	public static final String RESERVED_DEFAULT_PROFILE_NAME = "default";
 
 
 	protected final Log logger = LogFactory.getLog(getClass());