Merge pull request #30692 from terminux

* pr/30692:
  Polish "Validate overrides against CharsetMapperDefault.properties"
  Validate overrides against CharsetMapperDefault.properties

Closes gh-30692

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

@@ -27,6 +27,7 @@ import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Properties;
 import java.util.concurrent.Future;
 import java.util.concurrent.atomic.AtomicReference;
 
@@ -80,6 +81,8 @@ import org.springframework.boot.web.server.WebServerException;
 import org.springframework.boot.web.servlet.server.AbstractServletWebServerFactory;
 import org.springframework.boot.web.servlet.server.AbstractServletWebServerFactoryTests;
 import org.springframework.core.io.ByteArrayResource;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.support.PropertiesLoaderUtils;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
@@ -405,13 +408,15 @@ class TomcatServletWebServerFactoryTests extends AbstractServletWebServerFactory
 	}
 
 	@Test
-	void defaultLocaleCharsetMappingsAreOverridden() {
+	void defaultLocaleCharsetMappingsAreOverridden() throws IOException {
 		TomcatServletWebServerFactory factory = getFactory();
 		this.webServer = factory.getWebServer();
 		// override defaults, see org.apache.catalina.util.CharsetMapperDefault.properties
-		assertThat(getCharset(Locale.ENGLISH)).isEqualTo(StandardCharsets.UTF_8);
+		Properties charsetMapperDefault = PropertiesLoaderUtils
-		assertThat(getCharset(Locale.FRENCH)).isEqualTo(StandardCharsets.UTF_8);
+				.loadProperties(new ClassPathResource("CharsetMapperDefault.properties", CharsetMapper.class));
-		assertThat(getCharset(Locale.JAPANESE)).isEqualTo(StandardCharsets.UTF_8);
+		for (String language : charsetMapperDefault.stringPropertyNames()) {
+			assertThat(getCharset(new Locale(language))).isEqualTo(StandardCharsets.UTF_8);
+		}
 	}
 
 	@Test