Fix detection of dot-based resource bundle basenames

This commit makes sure that properties-based resource bundle location
with a dot is detected. It also harmonizes the description of the
configuration key as our support is not stricly matching the convention.

Closes gh-10092

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/context/MessageSourceAutoConfiguration.java

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -59,9 +59,10 @@ public class MessageSourceAutoConfiguration {
 	private static final Resource[] NO_RESOURCES = {};
 
 	/**
-	 * Comma-separated list of basenames, each following the ResourceBundle convention.
-	 * Essentially a fully-qualified classpath location. If it doesn't contain a package
-	 * qualifier (such as "org.mypackage"), it will be resolved from the classpath root.
+	 * Comma-separated list of basenames (essentially a fully-qualified classpath
+	 * location), each following the ResourceBundle convention with relaxed support for
+	 * slash based locations. If it doesn't contain a package qualifier (such as
+	 * "org.mypackage"), it will be resolved from the classpath root.
 	 */
 	private String basename = "messages";
 
@@ -180,9 +181,10 @@ public class MessageSourceAutoConfiguration {
 		}
 
 		private Resource[] getResources(ClassLoader classLoader, String name) {
+			String target = name.replace('.', '/');
 			try {
 				return new PathMatchingResourcePatternResolver(classLoader)
-						.getResources("classpath*:" + name + ".properties");
+						.getResources("classpath*:" + target + ".properties");
 			}
 			catch (Exception ex) {
 				return NO_RESOURCES;

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/context/MessageSourceAutoConfigurationTests.java

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 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.
@@ -60,8 +60,17 @@ public class MessageSourceAutoConfigurationTests {
 	}
 
 	@Test
-	public void testMessageSourceCreated() throws Exception {
+	public void propertiesBundleWithSlashIsDetected() {
 		load("spring.messages.basename:test/messages");
+		assertThat(this.context.getBeansOfType(MessageSource.class)).hasSize(1);
+		assertThat(this.context.getMessage("foo", null, "Foo message", Locale.UK))
+				.isEqualTo("bar");
+	}
+
+	@Test
+	public void propertiesBundleWithDotIsDetected() {
+		load("spring.messages.basename:test.messages");
+		assertThat(this.context.getBeansOfType(MessageSource.class)).hasSize(1);
 		assertThat(this.context.getMessage("foo", null, "Foo message", Locale.UK))
 				.isEqualTo("bar");
 	}

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -114,7 +114,7 @@ content into your application; rather pick only the properties that you need.
 
 	# INTERNATIONALIZATION ({sc-spring-boot-autoconfigure}/context/MessageSourceAutoConfiguration.{sc-ext}[MessageSourceAutoConfiguration])
 	spring.messages.always-use-message-format=false # Set whether to always apply the MessageFormat rules, parsing even messages without arguments.
-	spring.messages.basename=messages # Comma-separated list of basenames, each following the ResourceBundle convention.
+	spring.messages.basename=messages # Comma-separated list of basenames (essentially a fully-qualified classpath location), each following the ResourceBundle convention with relaxed support for slash based locations.
 	spring.messages.cache-seconds=-1 # Loaded resource bundle files cache expiration, in seconds. When set to -1, bundles are cached forever.
 	spring.messages.encoding=UTF-8 # Message bundles encoding.
 	spring.messages.fallback-to-system-locale=true # Set whether to fall back to the system Locale if no files for a specific Locale have been found.