Use TCCL at time of access for resource loading

Fixes gh-22119

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jdbc/DataSourceInitializer.java

@@ -67,8 +67,7 @@ class DataSourceInitializer {
 	DataSourceInitializer(DataSource dataSource, DataSourceProperties properties, ResourceLoader resourceLoader) {
 		this.dataSource = dataSource;
 		this.properties = properties;
-		this.resourceLoader = (resourceLoader != null) ? resourceLoader
-				: new DefaultResourceLoader(getClass().getClassLoader());
+		this.resourceLoader = (resourceLoader != null) ? resourceLoader : new DefaultResourceLoader(null);
 	}
 
 	/**

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/mustache/MustacheResourceTemplateLoader.java

@@ -47,7 +47,7 @@ public class MustacheResourceTemplateLoader implements TemplateLoader, ResourceL
 
 	private String charSet = "UTF-8";
 
-	private ResourceLoader resourceLoader = new DefaultResourceLoader(getClass().getClassLoader());
+	private ResourceLoader resourceLoader = new DefaultResourceLoader(null);
 
 	public MustacheResourceTemplateLoader() {
 	}

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/ClassLoaderFilesResourcePatternResolver.java

@@ -238,8 +238,7 @@ private static class ApplicationContextResourceLoader extends DefaultResourceLoa
 		private final Supplier<Collection<ProtocolResolver>> protocolResolvers;
 
 		ApplicationContextResourceLoader(Supplier<Collection<ProtocolResolver>> protocolResolvers) {
-			// Use the restart class loader
-			super(Thread.currentThread().getContextClassLoader());
+			super(null);
 			this.protocolResolvers = protocolResolvers;
 		}
 

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/context/SpringBootContextLoader.java

@@ -95,7 +95,7 @@ public ApplicationContext loadContext(MergedContextConfiguration config) throws
 			setActiveProfiles(environment, config.getActiveProfiles());
 		}
 		ResourceLoader resourceLoader = (application.getResourceLoader() != null) ? application.getResourceLoader()
-				: new DefaultResourceLoader(getClass().getClassLoader());
+				: new DefaultResourceLoader(null);
 		TestPropertySourceUtils.addPropertiesFilesToEnvironment(environment, resourceLoader,
 				config.getPropertySourceLocations());
 		TestPropertySourceUtils.addInlinedPropertiesToEnvironment(environment, getInlinedProperties(config));

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java

@@ -550,7 +550,7 @@ private Banner printBanner(ConfigurableEnvironment environment) {
 			return null;
 		}
 		ResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader
-				: new DefaultResourceLoader(getClassLoader());
+				: new DefaultResourceLoader(null);
 		SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner);
 		if (this.bannerMode == Mode.LOG) {
 			return bannerPrinter.print(environment, this.mainApplicationClass, logger);

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/config/ConfigFileApplicationListener.java

@@ -326,8 +326,7 @@ private class Loader {
 		Loader(ConfigurableEnvironment environment, ResourceLoader resourceLoader) {
 			this.environment = environment;
 			this.placeholdersResolver = new PropertySourcesPlaceholdersResolver(this.environment);
-			this.resourceLoader = (resourceLoader != null) ? resourceLoader
-					: new DefaultResourceLoader(getClass().getClassLoader());
+			this.resourceLoader = (resourceLoader != null) ? resourceLoader : new DefaultResourceLoader(null);
 			this.propertySourceLoaders = SpringFactoriesLoader.loadFactories(PropertySourceLoader.class,
 					getClass().getClassLoader());
 		}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/convert/StringToFileConverter.java

@@ -33,8 +33,7 @@
  */
 class StringToFileConverter implements Converter<String, File> {
 
-	private static final ResourceLoader resourceLoader = new DefaultResourceLoader(
-			StringToFileConverter.class.getClassLoader());
+	private static final ResourceLoader resourceLoader = new DefaultResourceLoader(null);
 
 	@Override
 	public File convert(String source) {