Add public variant getDeclaredMethods method

Add a public variant of `getDeclaredMethods` that defensively copies the
cached methods array. This is often more faster and more convenient
for users than calling `doWithLocalMethods`. We still retain most of the
benefits of the cache, namely fewer security manager calls and not as
many `Method` instances being created.

Closes gh-22580

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

@@ -230,7 +230,9 @@ public abstract class ReflectionUtils {
 		Assert.notNull(name, "Method name must not be null");
 		Class<?> searchType = clazz;
 		while (searchType != null) {
-			Method[] methods = (searchType.isInterface() ? searchType.getMethods() : getDeclaredMethods(searchType));
+			Method[] methods = searchType.isInterface() ?
+					searchType.getMethods() :
+					getDeclaredMethods(searchType, false);
 			for (Method method : methods) {
 				if (name.equals(method.getName()) &&
 						(paramTypes == null || Arrays.equals(paramTypes, method.getParameterTypes()))) {
@@ -308,7 +310,7 @@ public abstract class ReflectionUtils {
 	 * @see #doWithMethods
 	 */
 	public static void doWithLocalMethods(Class<?> clazz, MethodCallback mc) {
-		Method[] methods = getDeclaredMethods(clazz);
+		Method[] methods = getDeclaredMethods(clazz, false);
 		for (Method method : methods) {
 			try {
 				mc.doWith(method);
@@ -345,7 +347,7 @@ public abstract class ReflectionUtils {
 	 */
 	public static void doWithMethods(Class<?> clazz, MethodCallback mc, @Nullable MethodFilter mf) {
 		// Keep backing up the inheritance hierarchy.
-		Method[] methods = getDeclaredMethods(clazz);
+		Method[] methods = getDeclaredMethods(clazz, false);
 		for (Method method : methods) {
 			if (mf != null && !mf.matches(method)) {
 				continue;
@@ -429,16 +431,22 @@ public abstract class ReflectionUtils {
 	}
 
 	/**
-	 * This variant retrieves {@link Class#getDeclaredMethods()} from a local cache
-	 * in order to avoid the JVM's SecurityManager check and defensive array copying.
-	 * In addition, it also includes Java 8 default methods from locally implemented
-	 * interfaces, since those are effectively to be treated just like declared methods.
+	 * Variant of {@link Class#getDeclaredMethods()} that uses a local cache in
+	 * order to avoid the JVM's SecurityManager check and new Method instances.
+	 * In addition, it also includes Java 8 default methods from locally
+	 * implemented interfaces, since those are effectively to be treated just
+	 * like declared methods.
 	 * @param clazz the class to introspect
 	 * @return the cached array of methods
 	 * @throws IllegalStateException if introspection fails
+	 * @since 5.2
 	 * @see Class#getDeclaredMethods()
 	 */
-	private static Method[] getDeclaredMethods(Class<?> clazz) {
+	public static Method[] getDeclaredMethods(Class<?> clazz) {
+		return getDeclaredMethods(clazz, true);
+	}
+
+	private static Method[] getDeclaredMethods(Class<?> clazz, boolean defensive) {
 		Assert.notNull(clazz, "Class must not be null");
 		Method[] result = declaredMethodsCache.get(clazz);
 		if (result == null) {
@@ -464,7 +472,7 @@ public abstract class ReflectionUtils {
 						"] from ClassLoader [" + clazz.getClassLoader() + "]", ex);
 			}
 		}
-		return result;
+		return (result.length == 0 || !defensive) ? result : result.clone();
 	}
 
 	@Nullable

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -360,6 +360,13 @@ public class ReflectionUtilsTests {
 		assertThat(totalMs, Matchers.lessThan(10L));
 	}
 
+	@Test
+	public void getDecalredMethodsReturnsCopy() {
+		Method[] m1 = ReflectionUtils.getDeclaredMethods(A.class);
+		Method[] m2 = ReflectionUtils.getDeclaredMethods(A.class);
+		assertThat(m1, not(sameInstance(m2)));
+	}
+
 	private static class ListSavingMethodCallback implements ReflectionUtils.MethodCallback {
 
 		private List<String> methodNames = new LinkedList<>();