Avoid cloning empty Annotation array in TypeDescriptor (backport)

Closes gh-32405

Author: jhoeller

spring-core/src/main/java/org/springframework/core/convert/TypeDescriptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -52,8 +52,6 @@
 @SuppressWarnings("serial")
 public class TypeDescriptor implements Serializable {
 
-	private static final Annotation[] EMPTY_ANNOTATION_ARRAY = new Annotation[0];
-
 	private static final Map<Class<?>, TypeDescriptor> commonTypesCache = new HashMap<>(32);
 
 	private static final Class<?>[] CACHED_COMMON_TYPES = {
@@ -84,7 +82,7 @@ public class TypeDescriptor implements Serializable {
 	public TypeDescriptor(MethodParameter methodParameter) {
 		this.resolvableType = ResolvableType.forMethodParameter(methodParameter);
 		this.type = this.resolvableType.resolve(methodParameter.getNestedParameterType());
-		this.annotatedElement = new AnnotatedElementAdapter(methodParameter.getParameterIndex() == -1 ?
+		this.annotatedElement = AnnotatedElementAdapter.from(methodParameter.getParameterIndex() == -1 ?
 				methodParameter.getMethodAnnotations() : methodParameter.getParameterAnnotations());
 	}
 
@@ -96,7 +94,7 @@ public TypeDescriptor(MethodParameter methodParameter) {
 	public TypeDescriptor(Field field) {
 		this.resolvableType = ResolvableType.forField(field);
 		this.type = this.resolvableType.resolve(field.getType());
-		this.annotatedElement = new AnnotatedElementAdapter(field.getAnnotations());
+		this.annotatedElement = AnnotatedElementAdapter.from(field.getAnnotations());
 	}
 
 	/**
@@ -109,7 +107,7 @@ public TypeDescriptor(Property property) {
 		Assert.notNull(property, "Property must not be null");
 		this.resolvableType = ResolvableType.forMethodParameter(property.getMethodParameter());
 		this.type = this.resolvableType.resolve(property.getType());
-		this.annotatedElement = new AnnotatedElementAdapter(property.getAnnotations());
+		this.annotatedElement = AnnotatedElementAdapter.from(property.getAnnotations());
 	}
 
 	/**
@@ -125,7 +123,7 @@ public TypeDescriptor(Property property) {
 	public TypeDescriptor(ResolvableType resolvableType, @Nullable Class<?> type, @Nullable Annotation[] annotations) {
 		this.resolvableType = resolvableType;
 		this.type = (type != null ? type : resolvableType.toClass());
-		this.annotatedElement = new AnnotatedElementAdapter(annotations);
+		this.annotatedElement = AnnotatedElementAdapter.from(annotations);
 	}
 
 
@@ -547,12 +545,16 @@ public int hashCode() {
 	public String toString() {
 		StringBuilder builder = new StringBuilder();
 		for (Annotation ann : getAnnotations()) {
-			builder.append('@').append(ann.annotationType().getName()).append(' ');
+			builder.append('@').append(getName(ann.annotationType())).append(' ');
 		}
 		builder.append(getResolvableType());
 		return builder.toString();
 	}
 
+	private static String getName(Class<?> clazz) {
+		String canonicalName = clazz.getCanonicalName();
+		return (canonicalName != null ? canonicalName : clazz.getName());
+	}
 
 	/**
 	 * Create a new type descriptor for an object.
@@ -742,15 +744,23 @@ public static TypeDescriptor nested(Property property, int nestingLevel) {
 	 * @see AnnotatedElementUtils#isAnnotated(AnnotatedElement, Class)
 	 * @see AnnotatedElementUtils#getMergedAnnotation(AnnotatedElement, Class)
 	 */
-	private class AnnotatedElementAdapter implements AnnotatedElement, Serializable {
+	private static final class AnnotatedElementAdapter implements AnnotatedElement, Serializable {
+
+		private static final AnnotatedElementAdapter EMPTY = new AnnotatedElementAdapter(new Annotation[0]);
 
-		@Nullable
 		private final Annotation[] annotations;
 
-		public AnnotatedElementAdapter(@Nullable Annotation[] annotations) {
+		private AnnotatedElementAdapter(Annotation[] annotations) {
 			this.annotations = annotations;
 		}
 
+		private static AnnotatedElementAdapter from(@Nullable Annotation[] annotations) {
+			if (annotations == null || annotations.length == 0) {
+				return EMPTY;
+			}
+			return new AnnotatedElementAdapter(annotations);
+		}
+
 		@Override
 		public boolean isAnnotationPresent(Class<? extends Annotation> annotationClass) {
 			for (Annotation annotation : getAnnotations()) {
@@ -775,7 +785,7 @@ public <T extends Annotation> T getAnnotation(Class<T> annotationClass) {
 
 		@Override
 		public Annotation[] getAnnotations() {
-			return (this.annotations != null ? this.annotations.clone() : EMPTY_ANNOTATION_ARRAY);
+			return (isEmpty() ? this.annotations : this.annotations.clone());
 		}
 
 		@Override
@@ -784,7 +794,7 @@ public Annotation[] getDeclaredAnnotations() {
 		}
 
 		public boolean isEmpty() {
-			return ObjectUtils.isEmpty(this.annotations);
+			return (this.annotations.length == 0);
 		}
 
 		@Override
@@ -800,7 +810,7 @@ public int hashCode() {
 
 		@Override
 		public String toString() {
-			return TypeDescriptor.this.toString();
+			return "AnnotatedElementAdapter annotations=" + Arrays.toString(this.annotations);
 		}
 	}