ReloadableResourceBundleMessageSource sets file timestamp on merged holder

Issue: SPR-14583
(cherry picked from commit 03468fd)

Author: jhoeller

spring-context/src/main/java/org/springframework/context/support/ReloadableResourceBundleMessageSource.java

@@ -237,7 +237,7 @@ protected PropertiesHolder getMergedProperties(Locale locale) {
 			return mergedHolder;
 		}
 		Properties mergedProps = newProperties();
-		mergedHolder = new PropertiesHolder(mergedProps, -1);
+		long latestTimestamp = -1;
 		String[] basenames = StringUtils.toStringArray(getBasenameSet());
 		for (int i = basenames.length - 1; i >= 0; i--) {
 			List<String> filenames = calculateAllFilenames(basenames[i], locale);
@@ -246,9 +246,13 @@ protected PropertiesHolder getMergedProperties(Locale locale) {
 				PropertiesHolder propHolder = getProperties(filename);
 				if (propHolder.getProperties() != null) {
 					mergedProps.putAll(propHolder.getProperties());
+					if (propHolder.getFileTimestamp() > latestTimestamp) {
+						latestTimestamp = propHolder.getFileTimestamp();
+					}
 				}
 			}
 		}
+		mergedHolder = new PropertiesHolder(mergedProps, latestTimestamp);
 		PropertiesHolder existing = this.cachedMergedProperties.putIfAbsent(locale, mergedHolder);
 		if (existing != null) {
 			mergedHolder = existing;