Exclude sealed interfaces from auto-proxying (for JDK 17 compatibility)

Closes gh-27027

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

 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -19,7 +19,9 @@ package org.springframework.aop.framework;
 import java.lang.reflect.Array;
 import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
+import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.List;
 
 import org.springframework.aop.SpringProxy;
 import org.springframework.aop.TargetClassAware;
@@ -29,7 +31,9 @@ import org.springframework.aop.target.SingletonTargetSource;
 import org.springframework.core.DecoratingProxy;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
+import org.springframework.util.ReflectionUtils;
 
 /**
  * Utility methods for AOP proxy factories.
@@ -44,6 +48,11 @@ import org.springframework.util.ObjectUtils;
  */
 public abstract class AopProxyUtils {
 
+	// JDK 17 Class.isSealed() method available?
+	@Nullable
+	private static final Method isSealedMethod = ClassUtils.getMethodIfAvailable(Class.class, "isSealed");
+
+
 	/**
 	 * Obtain the singleton target object behind the given proxy, if any.
 	 * @param candidate the (potential) proxy to check
@@ -130,34 +139,23 @@ public abstract class AopProxyUtils {
 				specifiedInterfaces = advised.getProxiedInterfaces();
 			}
 		}
-		boolean addSpringProxy = !advised.isInterfaceProxied(SpringProxy.class);
-		boolean addAdvised = !advised.isOpaque() && !advised.isInterfaceProxied(Advised.class);
-		boolean addDecoratingProxy = (decoratingProxy && !advised.isInterfaceProxied(DecoratingProxy.class));
-		int nonUserIfcCount = 0;
-		if (addSpringProxy) {
-			nonUserIfcCount++;
-		}
-		if (addAdvised) {
-			nonUserIfcCount++;
-		}
-		if (addDecoratingProxy) {
-			nonUserIfcCount++;
+		List<Class<?>> proxiedInterfaces = new ArrayList<>(specifiedInterfaces.length + 3);
+		for (Class<?> ifc : specifiedInterfaces) {
+			// Only non-sealed interfaces are actually eligible for JDK proxying (on JDK 17)
+			if (isSealedMethod == null || Boolean.FALSE.equals(ReflectionUtils.invokeMethod(isSealedMethod, ifc))) {
+				proxiedInterfaces.add(ifc);
+			}
 		}
-		Class<?>[] proxiedInterfaces = new Class<?>[specifiedInterfaces.length + nonUserIfcCount];
-		System.arraycopy(specifiedInterfaces, 0, proxiedInterfaces, 0, specifiedInterfaces.length);
-		int index = specifiedInterfaces.length;
-		if (addSpringProxy) {
-			proxiedInterfaces[index] = SpringProxy.class;
-			index++;
+		if (!advised.isInterfaceProxied(SpringProxy.class)) {
+			proxiedInterfaces.add(SpringProxy.class);
 		}
-		if (addAdvised) {
-			proxiedInterfaces[index] = Advised.class;
-			index++;
+		if (!advised.isOpaque() && !advised.isInterfaceProxied(Advised.class)) {
+			proxiedInterfaces.add(Advised.class);
 		}
-		if (addDecoratingProxy) {
-			proxiedInterfaces[index] = DecoratingProxy.class;
+		if (decoratingProxy && !advised.isInterfaceProxied(DecoratingProxy.class)) {
+			proxiedInterfaces.add(DecoratingProxy.class);
 		}
-		return proxiedInterfaces;
+		return ClassUtils.toClassArray(proxiedInterfaces);
 	}
 
 	/**

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

 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -183,7 +183,7 @@ public class ProxyFactoryTests {
 	}
 
 	@Test
-	public void testGetsAllInterfaces() throws Exception {
+	public void testGetsAllInterfaces() {
 		// Extend to get new interface
 		class TestBeanSubclass extends TestBean implements Comparable<Object> {
 			@Override
@@ -240,6 +240,16 @@ public class ProxyFactoryTests {
 		assertThat(factory.countAdvicesOfType(NopInterceptor.class) == 2).isTrue();
 	}
 
+	@Test
+	public void testSealedInterfaceExclusion() {
+		// String implements ConstantDesc on JDK 12+, sealed as of JDK 17
+		ProxyFactory factory = new ProxyFactory(new String());
+		NopInterceptor di = new NopInterceptor();
+		factory.addAdvice(0, di);
+		Object proxy = factory.getProxy();
+		assertThat(proxy).isInstanceOf(CharSequence.class);
+	}
+
 	/**
 	 * Should see effect immediately on behavior.
 	 */