Add nullability annotations to core/spring-boot-test

See gh-46587

Author: mhalbritter

core/spring-boot-test/src/main/java/org/springframework/boot/test/context/AnnotatedClassFinder.java

@@ -22,6 +22,8 @@
 import java.util.Map;
 import java.util.Set;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider;
 import org.springframework.core.type.filter.AnnotationTypeFilter;
@@ -63,7 +65,7 @@ public AnnotatedClassFinder(Class<? extends Annotation> annotationType) {
 	 * @return the first {@link Class} annotated with the target annotation within the
 	 * hierarchy defined by the given {@code source} or {@code null} if none is found.
 	 */
-	public Class<?> findFromClass(Class<?> source) {
+	public @Nullable Class<?> findFromClass(Class<?> source) {
 		Assert.notNull(source, "'source' must not be null");
 		return findFromPackage(ClassUtils.getPackageName(source));
 	}
@@ -75,7 +77,7 @@ public Class<?> findFromClass(Class<?> source) {
 	 * @return the first {@link Class} annotated with the target annotation within the
 	 * hierarchy defined by the given {@code source} or {@code null} if none is found.
 	 */
-	public Class<?> findFromPackage(String source) {
+	public @Nullable Class<?> findFromPackage(String source) {
 		Assert.notNull(source, "'source' must not be null");
 		Class<?> configuration = cache.get(source);
 		if (configuration == null) {
@@ -85,13 +87,15 @@ public Class<?> findFromPackage(String source) {
 		return configuration;
 	}
 
-	private Class<?> scanPackage(String source) {
+	private @Nullable Class<?> scanPackage(String source) {
 		while (!source.isEmpty()) {
 			Set<BeanDefinition> components = this.scanner.findCandidateComponents(source);
 			if (!components.isEmpty()) {
 				Assert.state(components.size() == 1, () -> "Found multiple @" + this.annotationType.getSimpleName()
 						+ " annotated classes " + components);
-				return ClassUtils.resolveClassName(components.iterator().next().getBeanClassName(), null);
+				String beanClassName = components.iterator().next().getBeanClassName();
+				Assert.state(beanClassName != null, "'beanClassName' must not be null");
+				return ClassUtils.resolveClassName(beanClassName, null);
 			}
 			source = getParentPackage(source);
 		}

core/spring-boot-test/src/main/java/org/springframework/boot/test/context/FilteredClassLoader.java

@@ -27,6 +27,8 @@
 import java.util.Enumeration;
 import java.util.function.Predicate;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.SmartClassLoader;
 import org.springframework.core.io.ClassPathResource;
 
@@ -117,7 +119,7 @@ protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundE
 	}
 
 	@Override
-	public URL getResource(String name) {
+	public @Nullable URL getResource(String name) {
 		for (Predicate<String> filter : this.resourcesFilters) {
 			if (filter.test(name)) {
 				return null;
@@ -137,7 +139,7 @@ public Enumeration<URL> getResources(String name) throws IOException {
 	}
 
 	@Override
-	public InputStream getResourceAsStream(String name) {
+	public @Nullable InputStream getResourceAsStream(String name) {
 		for (Predicate<String> filter : this.resourcesFilters) {
 			if (filter.test(name)) {
 				return null;
@@ -147,7 +149,7 @@ public InputStream getResourceAsStream(String name) {
 	}
 
 	@Override
-	public Class<?> publicDefineClass(String name, byte[] b, ProtectionDomain protectionDomain) {
+	public Class<?> publicDefineClass(String name, byte[] b, @Nullable ProtectionDomain protectionDomain) {
 		for (Predicate<String> filter : this.classesFilters) {
 			if (filter.test(name)) {
 				throw new IllegalArgumentException(String.format("Defining class with name %s is not supported", name));

core/spring-boot-test/src/main/java/org/springframework/boot/test/context/ImportsContextCustomizer.java

@@ -24,6 +24,8 @@
 import java.util.Set;
 import java.util.stream.Collectors;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
@@ -156,6 +158,7 @@ static class ImportsSelector implements ImportSelector, BeanFactoryAware {
 
 		private static final String[] NO_IMPORTS = {};
 
+		@SuppressWarnings("NullAway.Init")
 		private ConfigurableListableBeanFactory beanFactory;
 
 		@Override
@@ -254,7 +257,7 @@ private boolean isFilteredAnnotation(String typeName) {
 			return ANNOTATION_FILTERS.stream().anyMatch((filter) -> filter.matches(typeName));
 		}
 
-		private Set<Object> determineImports(MergedAnnotations annotations, Class<?> testClass) {
+		private @Nullable Set<Object> determineImports(MergedAnnotations annotations, Class<?> testClass) {
 			Set<Object> determinedImports = new LinkedHashSet<>();
 			AnnotationMetadata metadata = AnnotationMetadata.introspect(testClass);
 			for (MergedAnnotation<Import> annotation : annotations.stream(Import.class).toList()) {
@@ -269,7 +272,7 @@ private Set<Object> determineImports(MergedAnnotations annotations, Class<?> tes
 			return determinedImports;
 		}
 
-		private Set<Object> determineImports(Class<?> source, AnnotationMetadata metadata) {
+		private @Nullable Set<Object> determineImports(Class<?> source, AnnotationMetadata metadata) {
 			if (DeterminableImports.class.isAssignableFrom(source)) {
 				// We can determine the imports
 				return ((DeterminableImports) instantiate(source)).determineImports(metadata);

core/spring-boot-test/src/main/java/org/springframework/boot/test/context/ImportsContextCustomizerFactory.java

@@ -19,6 +19,8 @@
 import java.lang.reflect.Method;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.AotDetector;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Import;
@@ -41,7 +43,7 @@
 class ImportsContextCustomizerFactory implements ContextCustomizerFactory {
 
 	@Override
-	public ContextCustomizer createContextCustomizer(Class<?> testClass,
+	public @Nullable ContextCustomizer createContextCustomizer(Class<?> testClass,
 			List<ContextConfigurationAttributes> configAttributes) {
 		if (AotDetector.useGeneratedArtifacts()) {
 			return null;

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

@@ -23,6 +23,8 @@
 import java.util.List;
 import java.util.function.Consumer;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.hint.ExecutableMode;
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.beans.BeanUtils;
@@ -105,6 +107,8 @@ public class SpringBootContextLoader extends AbstractContextLoader implements Ao
 	private static final Consumer<SpringApplication> ALREADY_CONFIGURED = (springApplication) -> {
 	};
 
+	private static final Object NONE = new Object();
+
 	@Override
 	public ApplicationContext loadContext(MergedContextConfiguration mergedConfig) throws Exception {
 		return loadContext(mergedConfig, Mode.STANDARD, null, null);
@@ -123,8 +127,8 @@ public ApplicationContext loadContextForAotRuntime(MergedContextConfiguration me
 	}
 
 	private ApplicationContext loadContext(MergedContextConfiguration mergedConfig, Mode mode,
-			ApplicationContextInitializer<ConfigurableApplicationContext> initializer, RuntimeHints runtimeHints)
-			throws Exception {
+			@Nullable ApplicationContextInitializer<ConfigurableApplicationContext> initializer,
+			@Nullable RuntimeHints runtimeHints) throws Exception {
 		assertHasClassesOrLocations(mergedConfig);
 		SpringBootTestAnnotation annotation = SpringBootTestAnnotation.get(mergedConfig);
 		String[] args = annotation.getArgs();
@@ -153,7 +157,7 @@ private void assertHasClassesOrLocations(MergedContextConfiguration mergedConfig
 						+ SpringVersion.getVersion() + ").");
 	}
 
-	private Method getMainMethod(MergedContextConfiguration mergedConfig, UseMainMethod useMainMethod) {
+	private @Nullable Method getMainMethod(MergedContextConfiguration mergedConfig, UseMainMethod useMainMethod) {
 		if (useMainMethod == UseMainMethod.NEVER) {
 			return null;
 		}
@@ -167,14 +171,16 @@ private Method getMainMethod(MergedContextConfiguration mergedConfig, UseMainMet
 				"Cannot use main method as no @SpringBootConfiguration-annotated class is available");
 		Method mainMethod = findMainMethod(springBootConfiguration);
 		Assert.state(mainMethod != null || useMainMethod == UseMainMethod.WHEN_AVAILABLE,
-				() -> "Main method not found on '%s'".formatted(springBootConfiguration.getName()));
+				() -> "Main method not found on '%s'"
+					.formatted((springBootConfiguration != null) ? springBootConfiguration.getName() : null));
 		return mainMethod;
 	}
 
-	private static Method findMainMethod(Class<?> type) {
+	private static @Nullable Method findMainMethod(@Nullable Class<?> type) {
 		Method mainMethod = (type != null) ? ReflectionUtils.findMethod(type, "main", String[].class) : null;
 		if (mainMethod == null && KotlinDetector.isKotlinPresent()) {
 			try {
+				Assert.state(type != null, "'type' must not be null");
 				Class<?> kotlinClass = ClassUtils.forName(type.getName() + "Kt", type.getClassLoader());
 				mainMethod = ReflectionUtils.findMethod(kotlinClass, "main", String[].class);
 			}
@@ -285,7 +291,7 @@ protected SpringApplication getSpringApplication() {
 	 * method if you need a custom environment.
 	 * @return a {@link ConfigurableEnvironment} instance
 	 */
-	protected ConfigurableEnvironment getEnvironment() {
+	protected @Nullable ConfigurableEnvironment getEnvironment() {
 		return null;
 	}
 
@@ -462,9 +468,9 @@ public void initialize(ConfigurableApplicationContext applicationContext) {
 	private static class ParentContextApplicationContextInitializer
 			implements ApplicationContextInitializer<ConfigurableApplicationContext> {
 
-		private final ApplicationContext parent;
+		private final @Nullable ApplicationContext parent;
 
-		ParentContextApplicationContextInitializer(ApplicationContext parent) {
+		ParentContextApplicationContextInitializer(@Nullable ApplicationContext parent) {
 			this.parent = parent;
 		}
 
@@ -507,15 +513,16 @@ private static class ContextLoaderHook implements SpringApplicationHook {
 
 		private final Mode mode;
 
-		private final ApplicationContextInitializer<ConfigurableApplicationContext> initializer;
+		private final @Nullable ApplicationContextInitializer<ConfigurableApplicationContext> initializer;
 
 		private final Consumer<SpringApplication> configurer;
 
 		private final List<ApplicationContext> contexts = Collections.synchronizedList(new ArrayList<>());
 
 		private final List<ApplicationContext> failedContexts = Collections.synchronizedList(new ArrayList<>());
 
-		ContextLoaderHook(Mode mode, ApplicationContextInitializer<ConfigurableApplicationContext> initializer,
+		ContextLoaderHook(Mode mode,
+				@Nullable ApplicationContextInitializer<ConfigurableApplicationContext> initializer,
 				Consumer<SpringApplication> configurer) {
 			this.mode = mode;
 			this.initializer = initializer;
@@ -530,6 +537,7 @@ public SpringApplicationRunListener getRunListener(SpringApplication application
 				public void starting(ConfigurableBootstrapContext bootstrapContext) {
 					ContextLoaderHook.this.configurer.accept(application);
 					if (ContextLoaderHook.this.mode == Mode.AOT_RUNTIME) {
+						Assert.state(ContextLoaderHook.this.initializer != null, "'initializer' must not be null");
 						application.addInitializers(
 								(AotApplicationContextInitializer<?>) ContextLoaderHook.this.initializer::initialize);
 					}
@@ -544,24 +552,24 @@ public void contextLoaded(ConfigurableApplicationContext context) {
 				}
 
 				@Override
-				public void failed(ConfigurableApplicationContext context, Throwable exception) {
+				public void failed(@Nullable ConfigurableApplicationContext context, Throwable exception) {
 					ContextLoaderHook.this.failedContexts.add(context);
 				}
 
 			};
 		}
 
-		private <T> ApplicationContext runMain(Runnable action) throws Exception {
+		private ApplicationContext runMain(Runnable action) throws Exception {
 			return run(() -> {
 				action.run();
-				return null;
+				return NONE;
 			});
 		}
 
-		private ApplicationContext run(ThrowingSupplier<ConfigurableApplicationContext> action) throws Exception {
+		private ApplicationContext run(ThrowingSupplier<?> action) throws Exception {
 			try {
-				ConfigurableApplicationContext context = SpringApplication.withHook(this, action);
-				if (context != null) {
+				Object result = SpringApplication.withHook(this, action);
+				if (result instanceof ApplicationContext context) {
 					return context;
 				}
 			}

core/spring-boot-test/src/main/java/org/springframework/boot/test/context/SpringBootTestAnnotation.java

@@ -19,6 +19,8 @@
 import java.util.Arrays;
 import java.util.Objects;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.test.context.SpringBootTest.UseMainMethod;
 import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
 import org.springframework.context.ConfigurableApplicationContext;
@@ -52,7 +54,7 @@ class SpringBootTestAnnotation implements ContextCustomizer {
 		this(TestContextAnnotationUtils.findMergedAnnotation(testClass, SpringBootTest.class));
 	}
 
-	private SpringBootTestAnnotation(SpringBootTest annotation) {
+	private SpringBootTestAnnotation(@Nullable SpringBootTest annotation) {
 		this.args = (annotation != null) ? annotation.args() : NO_ARGS;
 		this.webEnvironment = (annotation != null) ? annotation.webEnvironment() : WebEnvironment.NONE;
 		this.useMainMethod = (annotation != null) ? annotation.useMainMethod() : UseMainMethod.NEVER;

core/spring-boot-test/src/main/java/org/springframework/boot/test/context/SpringBootTestContextBootstrapper.java

@@ -25,6 +25,7 @@
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.SpringBootConfiguration;
 import org.springframework.boot.WebApplicationType;
@@ -287,7 +288,7 @@ private List<String> getAndProcessPropertySourceProperties(MergedContextConfigur
 	 * the bootstrapper class as a property.
 	 * @return the differentiator or {@code null}
 	 */
-	protected String getDifferentiatorPropertySourceProperty() {
+	protected @Nullable String getDifferentiatorPropertySourceProperty() {
 		return getClass().getName() + "=true";
 	}
 
@@ -320,22 +321,22 @@ else if (webEnvironment == WebEnvironment.NONE) {
 	 * @param testClass the source test class
 	 * @return the {@link WebEnvironment} or {@code null}
 	 */
-	protected WebEnvironment getWebEnvironment(Class<?> testClass) {
+	protected @Nullable WebEnvironment getWebEnvironment(Class<?> testClass) {
 		SpringBootTest annotation = getAnnotation(testClass);
 		return (annotation != null) ? annotation.webEnvironment() : null;
 	}
 
-	protected Class<?>[] getClasses(Class<?> testClass) {
+	protected Class<?> @Nullable [] getClasses(Class<?> testClass) {
 		SpringBootTest annotation = getAnnotation(testClass);
 		return (annotation != null) ? annotation.classes() : null;
 	}
 
-	protected String[] getProperties(Class<?> testClass) {
+	protected String @Nullable [] getProperties(Class<?> testClass) {
 		SpringBootTest annotation = getAnnotation(testClass);
 		return (annotation != null) ? annotation.properties() : null;
 	}
 
-	protected SpringBootTest getAnnotation(Class<?> testClass) {
+	protected @Nullable SpringBootTest getAnnotation(Class<?> testClass) {
 		return TestContextAnnotationUtils.findMergedAnnotation(testClass, SpringBootTest.class);
 	}