Merge branch '2.6.x' into 2.7.x

Closes gh-30542

Author: mhalbritter

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/tomcat/TomcatServletWebServerFactory.java

@@ -267,6 +267,7 @@ protected void prepareContext(Host host, ServletContextInitializer[] initializer
 	private void resetDefaultLocaleMapping(TomcatEmbeddedContext context) {
 		context.addLocaleEncodingMappingParameter(Locale.ENGLISH.toString(), DEFAULT_CHARSET.displayName());
 		context.addLocaleEncodingMappingParameter(Locale.FRENCH.toString(), DEFAULT_CHARSET.displayName());
+		context.addLocaleEncodingMappingParameter(Locale.JAPANESE.toString(), DEFAULT_CHARSET.displayName());
 	}
 
 	private void addLocaleMappings(TomcatEmbeddedContext context) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/tomcat/TomcatServletWebServerFactoryTests.java

@@ -410,6 +410,7 @@ void defaultLocaleCharsetMappingsAreOverridden() {
 		// override defaults, see org.apache.catalina.util.CharsetMapperDefault.properties
 		assertThat(getCharset(Locale.ENGLISH)).isEqualTo(StandardCharsets.UTF_8);
 		assertThat(getCharset(Locale.FRENCH)).isEqualTo(StandardCharsets.UTF_8);
+		assertThat(getCharset(Locale.JAPANESE)).isEqualTo(StandardCharsets.UTF_8);
 	}
 
 	@Test