Introduce getAliasedStringArray() in AnnotationAttributes

Issue: SPR-11393

spring-core/src/main/java/org/springframework/core/annotation/AnnotationAttributes.java

@@ -17,12 +17,14 @@
 package org.springframework.core.annotation;
 
 import java.lang.annotation.Annotation;
+import java.lang.reflect.AnnotatedElement;
 import java.lang.reflect.Array;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
 import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -131,6 +133,58 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 		return doGet(attributeName, String[].class);
 	}
 
+	/**
+	 * Get the value stored under the specified {@code attributeName} as an
+	 * array of strings, taking into account alias semantics defined via
+	 * {@link AliasFor @AliasFor}.
+	 * <p>If there is no value stored under the specified {@code attributeName}
+	 * but the attribute has an alias declared via {@code @AliasFor}, the
+	 * value of the alias will be returned.
+	 *
+	 * @param attributeName the name of the attribute to get; never
+	 * {@code null} or empty
+	 * @param annotationType the type of annotation represented by this
+	 * {@code AnnotationAttributes} instance; never {@code null}
+	 * @param annotationSource the source of the annotation represented by
+	 * this {@code AnnotationAttributes} (e.g., the {@link AnnotatedElement});
+	 * or {@code null} if unknown
+	 * @return the array of strings
+	 * @throws IllegalArgumentException if the attribute and its alias do
+	 * not exist or are not of type {@code String[]}
+	 * @throws AnnotationConfigurationException if the attribute and its
+	 * alias are both present with different non-empty values
+	 * @since 4.2
+	 */
+	public String[] getAliasedStringArray(String attributeName, Class<? extends Annotation> annotationType,
+			Object annotationSource) {
+
+		Assert.hasText(attributeName, "attributeName must not be null or empty");
+		Assert.notNull(annotationType, "annotationType must not be null");
+
+		String[] attributeValue = getStringArrayWithoutNullCheck(attributeName);
+		String aliasName = AnnotationUtils.getAttributeAliasMap(annotationType).get(attributeName);
+		String[] aliasValue = getStringArrayWithoutNullCheck(aliasName);
+		boolean attributeDeclared = !ObjectUtils.isEmpty(attributeValue);
+		boolean aliasDeclared = !ObjectUtils.isEmpty(aliasValue);
+
+		if (!ObjectUtils.nullSafeEquals(attributeValue, aliasValue) && attributeDeclared && aliasDeclared) {
+			String elementName = (annotationSource == null ? "unknown element" : annotationSource.toString());
+			String msg = String.format("In annotation [%s] declared on [%s], "
+					+ "attribute [%s] and its alias [%s] are present with values of [%s] and [%s], "
+					+ "but only one is permitted.", this.displayName, elementName, attributeName, aliasName,
+				ObjectUtils.nullSafeToString(attributeValue), ObjectUtils.nullSafeToString(aliasValue));
+			throw new AnnotationConfigurationException(msg);
+		}
+
+		if (!attributeDeclared) {
+			attributeValue = aliasValue;
+		}
+
+		assertAttributePresence(attributeName, aliasName, attributeValue);
+
+		return attributeValue;
+	}
+
 	/**
 	 * Get the value stored under the specified {@code attributeName} as a
 	 * boolean.
@@ -284,29 +338,52 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	 * @return the value
 	 * @throws IllegalArgumentException if the attribute does not exist or
 	 * if it is not of the expected type
-	 * @since 4.2
 	 */
 	@SuppressWarnings("unchecked")
 	private <T> T doGet(String attributeName, Class<T> expectedType) {
 		Assert.hasText(attributeName, "attributeName must not be null or empty");
 		Object value = get(attributeName);
-		if (value == null) {
+		assertAttributePresence(attributeName, value);
+		if (!expectedType.isInstance(value) && expectedType.isArray()
+				&& expectedType.getComponentType().isInstance(value)) {
+			Object array = Array.newInstance(expectedType.getComponentType(), 1);
+			Array.set(array, 0, value);
+			value = array;
+		}
+		assertAttributeType(attributeName, value, expectedType);
+		return (T) value;
+	}
+
+	private void assertAttributePresence(String attributeName, Object attributeValue) {
+		if (attributeValue == null) {
 			throw new IllegalArgumentException(String.format(
 				"Attribute '%s' not found in attributes for annotation [%s]", attributeName, this.displayName));
 		}
-		if (!expectedType.isInstance(value)) {
-			if (expectedType.isArray() && expectedType.getComponentType().isInstance(value)) {
-				Object array = Array.newInstance(expectedType.getComponentType(), 1);
-				Array.set(array, 0, value);
-				value = array;
-			}
-			else {
-				throw new IllegalArgumentException(String.format(
-					"Attribute '%s' is of type [%s], but [%s] was expected in attributes for annotation [%s]",
-					attributeName, value.getClass().getSimpleName(), expectedType.getSimpleName(), this.displayName));
-			}
+	}
+
+	private void assertAttributePresence(String attributeName, String aliasName, Object attributeValue) {
+		if (attributeValue == null) {
+			throw new IllegalArgumentException(String.format(
+				"Neither attribute '%s' nor its alias '%s' was found in attributes for annotation [%s]", attributeName,
+				aliasName, this.displayName));
 		}
-		return (T) value;
+	}
+
+	private void assertAttributeType(String attributeName, Object attributeValue, Class<?> expectedType) {
+		if (!expectedType.isInstance(attributeValue)) {
+			throw new IllegalArgumentException(String.format(
+				"Attribute '%s' is of type [%s], but [%s] was expected in attributes for annotation [%s]",
+				attributeName, attributeValue.getClass().getSimpleName(), expectedType.getSimpleName(),
+				this.displayName));
+		}
+	}
+
+	private String[] getStringArrayWithoutNullCheck(String attributeName) {
+		Object value = get(attributeName);
+		if (value != null) {
+			assertAttributeType(attributeName, value, String[].class);
+		}
+		return (String[]) value;
 	}
 
 	/**
@@ -354,7 +431,6 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 		return String.valueOf(value);
 	}
 
-
 	/**
 	 * Return an {@link AnnotationAttributes} instance based on the given map.
 	 * <p>If the map is already an {@code AnnotationAttributes} instance, it