Use same default ClassLoader in SpringFactoriesLoader

Prior to this commit, the loadFactoryNames() and loadFactories() methods
in SpringFactoriesLoader effectively used a different default
ClassLoader.

This commit ensures that the ClassLoader for SpringFactoriesLoader.class
is now consistently used as the default ClassLoader.

Closes gh-24992

spring-core/src/main/java/org/springframework/core/io/support/SpringFactoriesLoader.java

@@ -70,7 +70,7 @@ public final class SpringFactoriesLoader {
 
 	private static final Log logger = LogFactory.getLog(SpringFactoriesLoader.class);
 
-	private static final Map<ClassLoader, Map<String, List<String>>> cache = new ConcurrentReferenceHashMap<>();
+	static final Map<ClassLoader, Map<String, List<String>>> cache = new ConcurrentReferenceHashMap<>();
 
 
 	private SpringFactoriesLoader() {
@@ -124,11 +124,15 @@ public final class SpringFactoriesLoader {
 	 * @see #loadFactories
 	 */
 	public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
+		ClassLoader classLoaderToUse = classLoader;
+		if (classLoaderToUse == null) {
+			classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
+		}
 		String factoryTypeName = factoryType.getName();
-		return loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());
+		return loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());
 	}
 
-	private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
+	private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
 		Map<String, List<String>> result = cache.get(classLoader);
 		if (result != null) {
 			return result;
@@ -136,9 +140,7 @@ public final class SpringFactoriesLoader {
 
 		result = new HashMap<>();
 		try {
-			Enumeration<URL> urls = (classLoader != null ?
-					classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
-					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
+			Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);
 			while (urls.hasMoreElements()) {
 				URL url = urls.nextElement();
 				UrlResource resource = new UrlResource(url);

spring-core/src/test/java/org/springframework/core/io/support/SpringFactoriesLoaderTests.java

@@ -19,6 +19,8 @@ package org.springframework.core.io.support;
 import java.lang.reflect.Modifier;
 import java.util.List;
 
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -33,6 +35,23 @@ import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException
  */
 class SpringFactoriesLoaderTests {
 
+	@BeforeAll
+	static void clearCache() {
+		SpringFactoriesLoader.cache.clear();
+		assertThat(SpringFactoriesLoader.cache).isEmpty();
+	}
+
+	@AfterAll
+	static void checkCache() {
+		assertThat(SpringFactoriesLoader.cache).hasSize(1);
+	}
+
+	@Test
+	void loadFactoryNames() {
+		List<String> factoryNames = SpringFactoriesLoader.loadFactoryNames(DummyFactory.class, null);
+		assertThat(factoryNames).containsExactlyInAnyOrder(MyDummyFactory1.class.getName(), MyDummyFactory2.class.getName());
+	}
+
 	@Test
 	void loadFactoriesWithNoRegisteredImplementations() {
 		List<Integer> factories = SpringFactoriesLoader.loadFactories(Integer.class, null);