Add a classpath check for AOP Coroutines/Reactive conversion

Closes gh-32599

Author: sdeleuze

spring-aop/src/main/java/org/springframework/aop/framework/CglibAopProxy.java

@@ -102,6 +102,9 @@ class CglibAopProxy implements AopProxy, Serializable {
 
 	private static final String COROUTINES_FLOW_CLASS_NAME = "kotlinx.coroutines.flow.Flow";
 
+	private static final boolean coroutinesReactorPresent = ClassUtils.isPresent("kotlinx.coroutines.reactor.MonoKt",
+			CglibAopProxy.class.getClassLoader());;
+
 
 	/** The configuration used to configure this proxy. */
 	protected final AdvisedSupport advised;
@@ -421,7 +424,7 @@ private static Object processReturnType(
 			throw new AopInvocationException(
 					"Null return value from advice does not match primitive return type for: " + method);
 		}
-		if (KotlinDetector.isSuspendingFunction(method)) {
+		if (coroutinesReactorPresent && KotlinDetector.isSuspendingFunction(method)) {
 			return COROUTINES_FLOW_CLASS_NAME.equals(new MethodParameter(method, -1).getParameterType().getName()) ?
 					CoroutinesUtils.asFlow(returnValue) :
 					CoroutinesUtils.awaitSingleOrNull(returnValue, arguments[arguments.length - 1]);

spring-aop/src/main/java/org/springframework/aop/framework/JdkDynamicAopProxy.java

@@ -75,6 +75,9 @@ final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializa
 
 	private static final String COROUTINES_FLOW_CLASS_NAME = "kotlinx.coroutines.flow.Flow";
 
+	private static final boolean coroutinesReactorPresent = ClassUtils.isPresent("kotlinx.coroutines.reactor.MonoKt",
+			JdkDynamicAopProxy.class.getClassLoader());;
+
 	/** We use a static Log to avoid serialization issues. */
 	private static final Log logger = LogFactory.getLog(JdkDynamicAopProxy.class);
 
@@ -234,7 +237,7 @@ else if (retVal == null && returnType != void.class && returnType.isPrimitive())
 				throw new AopInvocationException(
 						"Null return value from advice does not match primitive return type for: " + method);
 			}
-			if (KotlinDetector.isSuspendingFunction(method)) {
+			if (coroutinesReactorPresent && KotlinDetector.isSuspendingFunction(method)) {
 				return COROUTINES_FLOW_CLASS_NAME.equals(new MethodParameter(method, -1).getParameterType().getName()) ?
 						CoroutinesUtils.asFlow(retVal) : CoroutinesUtils.awaitSingleOrNull(retVal, args[args.length - 1]);
 			}

spring-aop/src/main/java/org/springframework/aop/support/AopUtils.java

@@ -28,7 +28,6 @@
 import kotlin.coroutines.Continuation;
 import kotlin.coroutines.CoroutineContext;
 import kotlinx.coroutines.Job;
-import org.reactivestreams.Publisher;
 
 import org.springframework.aop.Advisor;
 import org.springframework.aop.AopInvocationException;
@@ -65,6 +64,9 @@
  */
 public abstract class AopUtils {
 
+	private static final boolean coroutinesReactorPresent = ClassUtils.isPresent("kotlinx.coroutines.reactor.MonoKt",
+			AopUtils.class.getClassLoader());;
+
 	/**
 	 * Check whether the given object is a JDK dynamic proxy or a CGLIB proxy.
 	 * <p>This method additionally checks if the given object is an instance
@@ -347,7 +349,7 @@ public static Object invokeJoinpointUsingReflection(@Nullable Object target, Met
 		// Use reflection to invoke the method.
 		try {
 			ReflectionUtils.makeAccessible(method);
-			return KotlinDetector.isSuspendingFunction(method) ?
+			return coroutinesReactorPresent && KotlinDetector.isSuspendingFunction(method) ?
 					KotlinDelegate.invokeSuspendingFunction(method, target, args) : method.invoke(target, args);
 		}
 		catch (InvocationTargetException ex) {
@@ -370,7 +372,7 @@ public static Object invokeJoinpointUsingReflection(@Nullable Object target, Met
 	 */
 	private static class KotlinDelegate {
 
-		public static Publisher<?> invokeSuspendingFunction(Method method, @Nullable Object target, Object... args) {
+		public static Object invokeSuspendingFunction(Method method, @Nullable Object target, Object... args) {
 			Continuation<?> continuation = (Continuation<?>) args[args.length -1];
 			Assert.state(continuation != null, "No Continuation available");
 			CoroutineContext context = continuation.getContext().minusKey(Job.Key);