Introduce ClassLoaderUtils.getClassLoader(Class)

Author: sbrannen

junit-jupiter-api/src/main/java/org/junit/jupiter/api/condition/MethodBasedCondition.java

@@ -66,10 +66,7 @@ Method getConditionMethod(String fullyQualifiedMethodName, ExtensionContext cont
 		String[] methodParts = ReflectionUtils.parseFullyQualifiedMethodName(fullyQualifiedMethodName);
 		String className = methodParts[0];
 		String methodName = methodParts[1];
-		ClassLoader classLoader = testClass.getClassLoader();
-		if (classLoader == null) {
-			classLoader = ClassLoaderUtils.getDefaultClassLoader();
-		}
+		ClassLoader classLoader = ClassLoaderUtils.getClassLoader(testClass);
 		Class<?> clazz = ReflectionUtils.tryToLoadClass(className, classLoader).getOrThrow(
 			cause -> new JUnitException(format("Could not load class [%s]", className), cause));
 		return findMethod(clazz, methodName);

junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/DefaultArgumentConverter.java

@@ -92,10 +92,8 @@ public final Object convert(Object source, Class<?> targetType, ParameterContext
 			Optional<StringToObjectConverter> converter = stringToObjectConverters.stream().filter(
 				candidate -> candidate.canConvert(targetTypeToUse)).findFirst();
 			if (converter.isPresent()) {
-				ClassLoader classLoader = context.getDeclaringExecutable().getDeclaringClass().getClassLoader();
-				if (classLoader == null) {
-					classLoader = ClassLoaderUtils.getDefaultClassLoader();
-				}
+				Class<?> declaringClass = context.getDeclaringExecutable().getDeclaringClass();
+				ClassLoader classLoader = ClassLoaderUtils.getClassLoader(declaringClass);
 				try {
 					return converter.get().convert((String) source, targetTypeToUse, classLoader);
 				}

junit-jupiter-params/src/main/java/org/junit/jupiter/params/provider/MethodArgumentsProvider.java

@@ -111,10 +111,7 @@ static Method findFactoryMethodByFullyQualifiedName(Class<?> testClass, Method t
 		String className = methodParts[0];
 		String methodName = methodParts[1];
 		String methodParameters = methodParts[2];
-		ClassLoader classLoader = testClass.getClassLoader();
-		if (classLoader == null) {
-			classLoader = ClassLoaderUtils.getDefaultClassLoader();
-		}
+		ClassLoader classLoader = ClassLoaderUtils.getClassLoader(testClass);
 		Class<?> clazz = loadRequiredClass(className, classLoader);
 
 		// Attempt to find an exact match first.

junit-platform-commons/src/main/java/org/junit/platform/commons/util/ClassLoaderUtils.java

@@ -36,6 +36,19 @@ private ClassLoaderUtils() {
 		/* no-op */
 	}
 
+	/**
+	 * Get the {@link ClassLoader} for the supplied {@link Class}, falling back
+	 * to the {@link #getDefaultClassLoader() default class loader} if the class
+	 * loader for the supplied class is {@code null}.
+	 * @param clazz the class for which to retrieve the class loader; never {@code null}
+	 * @since 1.10
+	 */
+	public static ClassLoader getClassLoader(Class<?> clazz) {
+		Preconditions.notNull(clazz, "Class must not be null");
+		ClassLoader classLoader = clazz.getClassLoader();
+		return (classLoader != null) ? classLoader : getDefaultClassLoader();
+	}
+
 	public static ClassLoader getDefaultClassLoader() {
 		try {
 			ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();

junit-platform-commons/src/main/java/org/junit/platform/commons/util/ReflectionUtils.java

@@ -1375,10 +1375,7 @@ private static Class<?>[] resolveParameterTypes(Class<?> clazz, String methodNam
 	}
 
 	private static Class<?> loadRequiredParameterType(Class<?> clazz, String methodName, String typeName) {
-		ClassLoader classLoader = clazz.getClassLoader();
-		if (classLoader == null) {
-			classLoader = ClassLoaderUtils.getDefaultClassLoader();
-		}
+		ClassLoader classLoader = ClassLoaderUtils.getClassLoader(clazz);
 
 		// @formatter:off
 		return tryToLoadClass(typeName, classLoader)

platform-tests/src/test/java/org/junit/platform/commons/util/ClassLoaderUtilsTests.java

@@ -10,6 +10,8 @@
 
 package org.junit.platform.commons.util;
 
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertSame;
 import static org.junit.jupiter.api.Assertions.assertThrows;
@@ -18,6 +20,7 @@
 
 import org.junit.jupiter.api.Test;
 import org.junit.platform.commons.PreconditionViolationException;
+import org.junit.platform.commons.test.TestClassLoader;
 
 /**
  * Unit tests for {@link ClassLoaderUtils}.
@@ -26,6 +29,52 @@
  */
 class ClassLoaderUtilsTests {
 
+	@Test
+	void getClassLoaderPreconditions() {
+		assertThatExceptionOfType(PreconditionViolationException.class)//
+				.isThrownBy(() -> ClassLoaderUtils.getClassLoader(null))//
+				.withMessage("Class must not be null");
+	}
+
+	@Test
+	void getClassLoaderForPrimitive() {
+		assertThat(int.class.getClassLoader()).isNull();
+		ClassLoader classLoader = ClassLoaderUtils.getClassLoader(int.class);
+		assertThat(classLoader).isSameAs(getClass().getClassLoader());
+	}
+
+	@Test
+	void getClassLoaderForWrapperType() {
+		assertThat(Byte.class.getClassLoader()).isNull();
+		ClassLoader classLoader = ClassLoaderUtils.getClassLoader(Byte.class);
+		assertThat(classLoader).isSameAs(getClass().getClassLoader());
+	}
+
+	@Test
+	void getClassLoaderForVoidType() {
+		assertThat(void.class.getClassLoader()).isNull();
+		ClassLoader classLoader = ClassLoaderUtils.getClassLoader(void.class);
+		assertThat(classLoader).isSameAs(getClass().getClassLoader());
+	}
+
+	@Test
+	void getClassLoaderForTestClass() {
+		assertThat(getClass().getClassLoader()).isNotNull();
+		ClassLoader classLoader = ClassLoaderUtils.getClassLoader(getClass());
+		assertThat(classLoader).isSameAs(getClass().getClassLoader());
+	}
+
+	@Test
+	void getClassLoaderForClassInDifferentClassLoader() throws Exception {
+		try (var testClassLoader = TestClassLoader.forClasses(getClass())) {
+			var testClass = testClassLoader.loadClass(getClass().getName());
+			assertThat(testClass.getClassLoader()).isSameAs(testClassLoader);
+
+			var classLoader = ClassLoaderUtils.getClassLoader(testClass);
+			assertThat(classLoader).isSameAs(testClassLoader);
+		}
+	}
+
 	@Test
 	void getDefaultClassLoaderWithExplicitContextClassLoader() {
 		var original = Thread.currentThread().getContextClassLoader();