Refine KotlinDetector usages and implementation

This commit refines KotlinDetector usages and implementation in order
to remove preliminary KotlinDetector#isKotlinReflectPresent invocations
and to ensure that KotlinDetector methods are implemented safely and
efficiently for such use case.

Closes gh-34275

spring-beans/src/main/java/org/springframework/beans/BeanUtils.java

@@ -186,7 +186,7 @@ public abstract class BeanUtils {
 		Assert.notNull(ctor, "Constructor must not be null");
 		try {
 			ReflectionUtils.makeAccessible(ctor);
-			if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(ctor.getDeclaringClass())) {
+			if (KotlinDetector.isKotlinType(ctor.getDeclaringClass())) {
 				return KotlinDelegate.instantiateClass(ctor, args);
 			}
 			else {
@@ -279,7 +279,7 @@ public abstract class BeanUtils {
 	 */
 	public static <T> @Nullable Constructor<T> findPrimaryConstructor(Class<T> clazz) {
 		Assert.notNull(clazz, "Class must not be null");
-		if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(clazz)) {
+		if (KotlinDetector.isKotlinType(clazz)) {
 			return KotlinDelegate.findPrimaryConstructor(clazz);
 		}
 		if (clazz.isRecord()) {

spring-beans/src/main/java/org/springframework/beans/factory/aot/InstanceSupplierCodeGenerator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -160,7 +160,7 @@ public class InstanceSupplierCodeGenerator {
 				registeredBean.getBeanName(), constructor, registeredBean.getBeanClass());
 
 		Class<?> publicType = descriptor.publicType();
-		if (KotlinDetector.isKotlinReflectPresent() && KotlinDelegate.hasConstructorWithOptionalParameter(publicType)) {
+		if (KotlinDetector.isKotlinType(publicType) && KotlinDelegate.hasConstructorWithOptionalParameter(publicType)) {
 			return generateCodeForInaccessibleConstructor(descriptor,
 					hints -> hints.registerType(publicType, MemberCategory.INVOKE_DECLARED_CONSTRUCTORS));
 		}
@@ -408,7 +408,6 @@ public class InstanceSupplierCodeGenerator {
 	private static class KotlinDelegate {
 
 		public static boolean hasConstructorWithOptionalParameter(Class<?> beanClass) {
-			if (KotlinDetector.isKotlinType(beanClass)) {
 			KClass<?> kClass = JvmClassMappingKt.getKotlinClass(beanClass);
 			for (KFunction<?> constructor : kClass.getConstructors()) {
 				for (KParameter parameter : constructor.getParameters()) {
@@ -417,7 +416,6 @@ public class InstanceSupplierCodeGenerator {
 					}
 				}
 			}
-			}
 			return false;
 		}
 	}

spring-beans/src/main/java/org/springframework/beans/factory/config/DependencyDescriptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -163,9 +163,7 @@ public class DependencyDescriptor extends InjectionPoint implements Serializable
 
 		if (this.field != null) {
 			return !(this.field.getType() == Optional.class || hasNullableAnnotation() ||
-					(KotlinDetector.isKotlinReflectPresent() &&
+					(KotlinDetector.isKotlinType(this.field.getDeclaringClass()) && KotlinDelegate.isNullable(this.field)));
-							KotlinDetector.isKotlinType(this.field.getDeclaringClass()) &&
-							KotlinDelegate.isNullable(this.field)));
 		}
 		else {
 			return !obtainMethodParameter().isOptional();

spring-beans/src/main/java/org/springframework/beans/factory/support/ConstructorResolver.java

@@ -624,7 +624,7 @@ class ConstructorResolver {
 						"Invalid factory method '" + mbd.getFactoryMethodName() + "' on class [" +
 						factoryClass.getName() + "]: needs to have a non-void return type!");
 			}
-			else if (KotlinDetector.isKotlinPresent() && KotlinDetector.isSuspendingFunction(factoryMethodToUse)) {
+			else if (KotlinDetector.isSuspendingFunction(factoryMethodToUse)) {
 				throw new BeanCreationException(mbd.getResourceDescription(), beanName,
 						"Invalid factory method '" + mbd.getFactoryMethodName() + "' on class [" +
 								factoryClass.getName() + "]: suspending functions are not supported!");

spring-context/src/main/java/org/springframework/cache/interceptor/CacheAspectSupport.java

@@ -1092,7 +1092,7 @@ public abstract class CacheAspectSupport extends AbstractCacheInvoker
 									() -> Mono.from(adapter.toPublisher(invokeOperation(invoker))).toFuture())));
 				}
 			}
-			if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isSuspendingFunction(method)) {
+			if (KotlinDetector.isSuspendingFunction(method)) {
 				return Mono.fromFuture(cache.retrieve(key, () -> {
 					Mono<?> mono = ((Mono<?>) invokeOperation(invoker));
 					if (mono == null) {

spring-context/src/main/java/org/springframework/scheduling/annotation/ScheduledAnnotationReactiveSupport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -81,7 +81,7 @@ abstract class ScheduledAnnotationReactiveSupport {
 	 * Kotlin coroutines bridge are not present at runtime
 	 */
 	public static boolean isReactive(Method method) {
-		if (KotlinDetector.isKotlinPresent() && KotlinDetector.isSuspendingFunction(method)) {
+		if (KotlinDetector.isSuspendingFunction(method)) {
 			// Note that suspending functions declared without args have a single Continuation
 			// parameter in reflective inspection
 			Assert.isTrue(method.getParameterCount() == 1,
@@ -138,7 +138,7 @@ abstract class ScheduledAnnotationReactiveSupport {
 	 * to a {@code Flux} with a checkpoint String, allowing for better debugging.
 	 */
 	static Publisher<?> getPublisherFor(Method method, Object bean) {
-		if (KotlinDetector.isKotlinPresent() && KotlinDetector.isSuspendingFunction(method)) {
+		if (KotlinDetector.isSuspendingFunction(method)) {
 			return CoroutinesUtils.invokeSuspendingFunction(method, bean, (Object[]) method.getParameters());
 		}
 

spring-core/src/main/java/org/springframework/core/KotlinDetector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,7 +24,8 @@ import org.jspecify.annotations.Nullable;
 import org.springframework.util.ClassUtils;
 
 /**
- * A common delegate for detecting Kotlin's presence and for identifying Kotlin types.
+ * A common delegate for detecting Kotlin's presence and for identifying Kotlin types. All the methods of this class
+ * can be safely used without any preliminary classpath checks.
  *
  * @author Juergen Hoeller
  * @author Sebastien Deleuze
@@ -37,6 +38,8 @@ public abstract class KotlinDetector {
 
 	private static final @Nullable Class<? extends Annotation> kotlinJvmInline;
 
+	private static final @Nullable Class<?> kotlinCoroutineContinuation;
+
 	// For ConstantFieldFeature compliance, otherwise could be deduced from kotlinMetadata
 	private static final boolean kotlinPresent;
 
@@ -46,6 +49,7 @@ public abstract class KotlinDetector {
 		ClassLoader classLoader = KotlinDetector.class.getClassLoader();
 		Class<?> metadata = null;
 		Class<?> jvmInline = null;
+		Class<?> coroutineContinuation = null;
 		try {
 			metadata = ClassUtils.forName("kotlin.Metadata", classLoader);
 			try {
@@ -54,14 +58,21 @@ public abstract class KotlinDetector {
 			catch (ClassNotFoundException ex) {
 				// JVM inline support not available
 			}
+			try {
+				coroutineContinuation = ClassUtils.forName("kotlin.coroutines.Continuation", classLoader);
+			}
+			catch (ClassNotFoundException ex) {
+				// Coroutines support not available
+			}
 		}
 		catch (ClassNotFoundException ex) {
 			// Kotlin API not available - no Kotlin support
 		}
 		kotlinMetadata = (Class<? extends Annotation>) metadata;
 		kotlinPresent = (kotlinMetadata != null);
-		kotlinReflectPresent = kotlinPresent && ClassUtils.isPresent("kotlin.reflect.full.KClasses", classLoader);
+		kotlinReflectPresent = ClassUtils.isPresent("kotlin.reflect.full.KClasses", classLoader);
 		kotlinJvmInline = (Class<? extends Annotation>) jvmInline;
+		kotlinCoroutineContinuation = coroutineContinuation;
 	}
 
 
@@ -89,7 +100,7 @@ public abstract class KotlinDetector {
 	 * as invokedynamic has become the default method for lambda generation.
 	 */
 	public static boolean isKotlinType(Class<?> clazz) {
-		return (kotlinMetadata != null && clazz.getDeclaredAnnotation(kotlinMetadata) != null);
+		return (kotlinPresent && clazz.getDeclaredAnnotation(kotlinMetadata) != null);
 	}
 
 	/**
@@ -97,14 +108,12 @@ public abstract class KotlinDetector {
 	 * @since 5.3
 	 */
 	public static boolean isSuspendingFunction(Method method) {
-		if (KotlinDetector.isKotlinType(method.getDeclaringClass())) {
+		if (kotlinCoroutineContinuation == null) {
-			Class<?>[] types = method.getParameterTypes();
-			if (types.length > 0 && "kotlin.coroutines.Continuation".equals(types[types.length - 1].getName())) {
-				return true;
-			}
-		}
 			return false;
 		}
+		int parameterCount = method.getParameterCount();
+		return (parameterCount > 0 && method.getParameterTypes()[parameterCount - 1] == kotlinCoroutineContinuation);
+	}
 
 	/**
 	 * Determine whether the given {@code Class} is an inline class

spring-core/src/main/java/org/springframework/core/MethodParameter.java

@@ -396,9 +396,7 @@ public class MethodParameter {
 	 */
 	public boolean isOptional() {
 		return (getParameterType() == Optional.class || hasNullableAnnotation() ||
-				(KotlinDetector.isKotlinReflectPresent() &&
+				(KotlinDetector.isKotlinType(getContainingClass()) && KotlinDelegate.isOptional(this)));
-						KotlinDetector.isKotlinType(getContainingClass()) &&
-						KotlinDelegate.isOptional(this)));
 	}
 
 	/**
@@ -508,7 +506,7 @@ public class MethodParameter {
 			if (this.parameterIndex < 0) {
 				Method method = getMethod();
 				paramType = (method != null ?
-						(KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(getContainingClass()) ?
+						(KotlinDetector.isKotlinType(getContainingClass()) ?
 								KotlinDelegate.getGenericReturnType(method) : method.getGenericReturnType()) : void.class);
 			}
 			else {
@@ -536,7 +534,7 @@ public class MethodParameter {
 			if (method == null) {
 				return void.class;
 			}
-			if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(getContainingClass())) {
+			if (KotlinDetector.isKotlinType(getContainingClass())) {
 				return KotlinDelegate.getReturnType(method);
 			}
 			return method.getReturnType();

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

@@ -374,7 +374,7 @@ public class SpringFactoriesLoader {
 
 		T instantiate(@Nullable ArgumentResolver argumentResolver) throws Exception {
 			Object[] args = resolveArgs(argumentResolver);
-			if (isKotlinType(this.constructor.getDeclaringClass())) {
+			if (KotlinDetector.isKotlinType(this.constructor.getDeclaringClass())) {
 				return KotlinDelegate.instantiate(this.constructor, args);
 			}
 			return this.constructor.newInstance(args);
@@ -408,14 +408,10 @@ public class SpringFactoriesLoader {
 		}
 
 		private static @Nullable Constructor<?> findPrimaryKotlinConstructor(Class<?> factoryImplementationClass) {
-			return (isKotlinType(factoryImplementationClass) ?
+			return (KotlinDetector.isKotlinType(factoryImplementationClass) ?
 					KotlinDelegate.findPrimaryConstructor(factoryImplementationClass) : null);
 		}
 
-		private static boolean isKotlinType(Class<?> factoryImplementationClass) {
-			return KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(factoryImplementationClass);
-		}
-
 		private static @Nullable Constructor<?> findSingleConstructor(Constructor<?>[] constructors) {
 			return (constructors.length == 1 ? constructors[0] : null);
 		}

spring-expression/src/main/java/org/springframework/expression/spel/support/ReflectivePropertyAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -558,8 +558,7 @@ public class ReflectivePropertyAccessor implements PropertyAccessor {
 
 	private static boolean isKotlinProperty(Method method, String methodSuffix) {
 		Class<?> clazz = method.getDeclaringClass();
-		return KotlinDetector.isKotlinReflectPresent() &&
+		return KotlinDetector.isKotlinType(clazz) &&
-				KotlinDetector.isKotlinType(clazz) &&
 				KotlinDelegate.isKotlinProperty(method, methodSuffix);
 	}
 

spring-web/src/main/java/org/springframework/http/converter/json/Jackson2ObjectMapperBuilder.java

@@ -868,8 +868,7 @@ public class Jackson2ObjectMapperBuilder {
 			// jackson-datatype-jsr310 not available
 		}
 
-		// Kotlin present?
+		if (KotlinDetector.isKotlinReflectPresent()) {
-		if (KotlinDetector.isKotlinPresent()) {
 			try {
 				Class<? extends Module> kotlinModuleClass = (Class<? extends Module>)
 						ClassUtils.forName("com.fasterxml.jackson.module.kotlin.KotlinModule", this.moduleClassLoader);

spring-web/src/main/java/org/springframework/web/method/annotation/AbstractNamedValueMethodArgumentResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -103,8 +103,7 @@ public abstract class AbstractNamedValueMethodArgumentResolver implements Handle
 
 		NamedValueInfo namedValueInfo = getNamedValueInfo(parameter);
 		MethodParameter nestedParameter = parameter.nestedIfOptional();
-		boolean hasDefaultValue = KotlinDetector.isKotlinReflectPresent() &&
+		boolean hasDefaultValue = KotlinDetector.isKotlinType(parameter.getDeclaringClass()) &&
-				KotlinDetector.isKotlinType(parameter.getDeclaringClass()) &&
 				KotlinDelegate.hasDefaultValue(nestedParameter);
 
 		Object resolvedName = resolveEmbeddedValuesAndExpressions(namedValueInfo.name);
@@ -276,7 +275,7 @@ public abstract class AbstractNamedValueMethodArgumentResolver implements Handle
 
 		WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);
 		Class<?> parameterType = parameter.getParameterType();
-		if (KotlinDetector.isKotlinPresent() && KotlinDetector.isInlineClass(parameterType)) {
+		if (KotlinDetector.isInlineClass(parameterType)) {
 			Constructor<?> ctor = BeanUtils.findPrimaryConstructor(parameterType);
 			if (ctor != null) {
 				parameterType = ctor.getParameterTypes()[0];

spring-web/src/main/java/org/springframework/web/method/support/InvocableHandlerMethod.java

@@ -242,14 +242,12 @@ public class InvocableHandlerMethod extends HandlerMethod {
 	protected @Nullable Object doInvoke(@Nullable Object... args) throws Exception {
 		Method method = getBridgedMethod();
 		try {
-			if (KotlinDetector.isKotlinReflectPresent()) {
+			if (KotlinDetector.isKotlinType(method.getDeclaringClass())) {
 				if (KotlinDetector.isSuspendingFunction(method)) {
 					return invokeSuspendingFunction(method, getBean(), args);
 				}
-				else if (KotlinDetector.isKotlinType(method.getDeclaringClass())) {
 				return KotlinDelegate.invokeFunction(method, getBean(), args);
 			}
-			}
 			return method.invoke(getBean(), args);
 		}
 		catch (IllegalArgumentException ex) {

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/InvocableHandlerMethod.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -191,12 +191,9 @@ public class InvocableHandlerMethod extends HandlerMethod {
 			Method method = getBridgedMethod();
 			boolean isSuspendingFunction = KotlinDetector.isSuspendingFunction(method);
 			try {
-				if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(method.getDeclaringClass())) {
+				value = (KotlinDetector.isKotlinType(method.getDeclaringClass()) ?
-					value = KotlinDelegate.invokeFunction(method, getBean(), args, isSuspendingFunction, exchange);
+						KotlinDelegate.invokeFunction(method, getBean(), args, isSuspendingFunction, exchange) :
-				}
+						method.invoke(getBean(), args));
-				else {
-					value = method.invoke(getBean(), args);
-				}
 			}
 			catch (IllegalArgumentException ex) {
 				assertTargetBean(getBridgedMethod(), getBean(), args);

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/AbstractNamedValueArgumentResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -195,7 +195,7 @@ public abstract class AbstractNamedValueArgumentResolver extends HandlerMethodAr
 
 		WebDataBinder binder = bindingContext.createDataBinder(exchange, namedValueInfo.name);
 		Class<?> parameterType = parameter.getParameterType();
-		if (KotlinDetector.isKotlinPresent() && KotlinDetector.isInlineClass(parameterType)) {
+		if (KotlinDetector.isInlineClass(parameterType)) {
 			Constructor<?> ctor = BeanUtils.findPrimaryConstructor(parameterType);
 			if (ctor != null) {
 				parameterType = ctor.getParameterTypes()[0];
@@ -222,8 +222,7 @@ public abstract class AbstractNamedValueArgumentResolver extends HandlerMethodAr
 
 		return Mono.fromSupplier(() -> {
 			Object value = null;
-			boolean hasDefaultValue = KotlinDetector.isKotlinReflectPresent() &&
+			boolean hasDefaultValue = KotlinDetector.isKotlinType(parameter.getDeclaringClass()) &&
-					KotlinDetector.isKotlinType(parameter.getDeclaringClass()) &&
 					KotlinDelegate.hasDefaultValue(parameter);
 			if (namedValueInfo.defaultValue != null) {
 				value = resolveEmbeddedValuesAndExpressions(namedValueInfo.defaultValue);