Introduce isLambdaClass() as a public utility in ClassUtils

This commit extracts isLambda() from AopProxyUtils and makes it
publicly available as ClassUtils.isLambdaClass().

This is a prerequisite for gh-28209.

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

@@ -134,7 +134,7 @@ public abstract class AopProxyUtils {
 				if (targetClass.isInterface()) {
 					advised.setInterfaces(targetClass);
 				}
-				else if (Proxy.isProxyClass(targetClass) || isLambda(targetClass)) {
+				else if (Proxy.isProxyClass(targetClass) || ClassUtils.isLambdaClass(targetClass)) {
 					advised.setInterfaces(targetClass.getInterfaces());
 				}
 				specifiedInterfaces = advised.getProxiedInterfaces();
@@ -245,18 +245,4 @@ public abstract class AopProxyUtils {
 		return arguments;
 	}
 
-	/**
-	 * Determine if the supplied {@link Class} is a JVM-generated implementation
-	 * class for a lambda expression or method reference.
-	 * <p>This method makes a best-effort attempt at determining this, based on
-	 * checks that work on modern, main stream JVMs.
-	 * @param clazz the class to check
-	 * @return {@code true} if the class is a lambda implementation class
-	 * @since 5.3.16
-	 */
-	static boolean isLambda(Class<?> clazz) {
-		return (clazz.isSynthetic() && (clazz.getSuperclass() == Object.class) &&
-				(clazz.getInterfaces().length > 0) && clazz.getName().contains("$$Lambda"));
-	}
-
 }

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

@@ -21,6 +21,7 @@ import java.lang.reflect.Proxy;
 
 import org.springframework.aop.SpringProxy;
 import org.springframework.core.NativeDetector;
+import org.springframework.util.ClassUtils;
 
 /**
  * Default {@link AopProxyFactory} implementation, creating either a CGLIB proxy
@@ -60,7 +61,7 @@ public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
 				throw new AopConfigException("TargetSource cannot determine target class: " +
 						"Either an interface or a target is required for proxy creation.");
 			}
-			if (targetClass.isInterface() || Proxy.isProxyClass(targetClass) || AopProxyUtils.isLambda(targetClass)) {
+			if (targetClass.isInterface() || Proxy.isProxyClass(targetClass) || ClassUtils.isLambdaClass(targetClass)) {
 				return new JdkDynamicAopProxy(config);
 			}
 			return new ObjenesisCglibAopProxy(config);

spring-aop/src/test/java/org/springframework/aop/framework/AopProxyUtilsTests.java

@@ -19,7 +19,6 @@ package org.springframework.aop.framework;
 import java.lang.reflect.Proxy;
 import java.util.Arrays;
 import java.util.List;
-import java.util.function.Supplier;
 
 import org.junit.jupiter.api.Test;
 
@@ -134,61 +133,4 @@ public class AopProxyUtilsTests {
 				AopProxyUtils.proxiedUserInterfaces(proxy));
 	}
 
-	@Test
-	void isLambda() {
-		assertIsLambda(AopProxyUtilsTests.staticLambdaExpression);
-		assertIsLambda(AopProxyUtilsTests::staticStringFactory);
-
-		assertIsLambda(this.instanceLambdaExpression);
-		assertIsLambda(this::instanceStringFactory);
-	}
-
-	@Test
-	void isNotLambda() {
-		assertIsNotLambda(new EnigmaSupplier());
-
-		assertIsNotLambda(new Supplier<String>() {
-			@Override
-			public String get() {
-				return "anonymous inner class";
-			}
-		});
-
-		assertIsNotLambda(new Fake$$LambdaSupplier());
-	}
-
-	private static void assertIsLambda(Supplier<String> supplier) {
-		assertThat(AopProxyUtils.isLambda(supplier.getClass())).isTrue();
-	}
-
-	private static void assertIsNotLambda(Supplier<String> supplier) {
-		assertThat(AopProxyUtils.isLambda(supplier.getClass())).isFalse();
-	}
-
-	private static final Supplier<String> staticLambdaExpression = () -> "static lambda expression";
-
-	private final Supplier<String> instanceLambdaExpression = () -> "instance lambda expressions";
-
-	private static String staticStringFactory() {
-		return "static string factory";
-	}
-
-	private String instanceStringFactory() {
-		return "instance string factory";
-	}
-
-	private static class EnigmaSupplier implements Supplier<String> {
-		@Override
-		public String get() {
-			return "enigma";
-		}
-	}
-
-	private static class Fake$$LambdaSupplier implements Supplier<String> {
-		@Override
-		public String get() {
-			return "fake lambda";
-		}
-	}
-
 }

spring-core/src/main/java/org/springframework/util/ClassUtils.java

@@ -842,6 +842,20 @@ public abstract class ClassUtils {
 		return (clazz.isMemberClass() && !Modifier.isStatic(clazz.getModifiers()));
 	}
 
+	/**
+	 * Determine if the supplied {@link Class} is a JVM-generated implementation
+	 * class for a lambda expression or method reference.
+	 * <p>This method makes a best-effort attempt at determining this, based on
+	 * checks that work on modern, mainstream JVMs.
+	 * @param clazz the class to check
+	 * @return {@code true} if the class is a lambda implementation class
+	 * @since 5.3.19
+	 */
+	public static boolean isLambdaClass(Class<?> clazz) {
+		return (clazz.isSynthetic() && (clazz.getSuperclass() == Object.class) &&
+				(clazz.getInterfaces().length > 0) && clazz.getName().contains("$$Lambda"));
+	}
+
 	/**
 	 * Check whether the given object is a CGLIB proxy.
 	 * @param object the object to check

spring-core/src/test/java/org/springframework/util/ClassUtilsTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -31,6 +31,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Set;
+import java.util.function.Supplier;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Nested;
@@ -408,6 +409,29 @@ class ClassUtilsTests {
 		assertThat(ClassUtils.isPrimitiveOrWrapper(type)).isTrue();
 	}
 
+	@Test
+	void isLambda() {
+		assertIsLambda(ClassUtilsTests.staticLambdaExpression);
+		assertIsLambda(ClassUtilsTests::staticStringFactory);
+
+		assertIsLambda(this.instanceLambdaExpression);
+		assertIsLambda(this::instanceStringFactory);
+	}
+
+	@Test
+	void isNotLambda() {
+		assertIsNotLambda(new EnigmaSupplier());
+
+		assertIsNotLambda(new Supplier<String>() {
+			@Override
+			public String get() {
+				return "anonymous inner class";
+			}
+		});
+
+		assertIsNotLambda(new Fake$$LambdaSupplier());
+	}
+
 
 	@Nested
 	class GetStaticMethodTests {
@@ -500,4 +524,38 @@ class ClassUtilsTests {
 		}
 	}
 
+	private static void assertIsLambda(Supplier<String> supplier) {
+		assertThat(ClassUtils.isLambdaClass(supplier.getClass())).isTrue();
+	}
+
+	private static void assertIsNotLambda(Supplier<String> supplier) {
+		assertThat(ClassUtils.isLambdaClass(supplier.getClass())).isFalse();
+	}
+
+	private static final Supplier<String> staticLambdaExpression = () -> "static lambda expression";
+
+	private final Supplier<String> instanceLambdaExpression = () -> "instance lambda expressions";
+
+	private static String staticStringFactory() {
+		return "static string factory";
+	}
+
+	private String instanceStringFactory() {
+		return "instance string factory";
+	}
+
+	private static class EnigmaSupplier implements Supplier<String> {
+		@Override
+		public String get() {
+			return "enigma";
+		}
+	}
+
+	private static class Fake$$LambdaSupplier implements Supplier<String> {
+		@Override
+		public String get() {
+			return "fake lambda";
+		}
+	}
+
 }