Support nested annotations in AnnotationAttributes

This commit introduces support in AnnotationAttributes for retrieving
nested annotations that is on par with the existing type-safe support
for retrieving nested AnnotationAttributes.

Issue: SPR-13074

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

@@ -205,6 +205,8 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	/**
 	 * Get the {@link AnnotationAttributes} stored under the specified
 	 * {@code attributeName}.
+	 * <p>Note: if you expect an actual annotation, invoke
+	 * {@link #getAnnotation(String, Class)} instead.
 	 * @param attributeName the name of the attribute to get; never
 	 * {@code null} or empty
 	 * @return the {@code AnnotationAttributes}
@@ -215,12 +217,29 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 		return doGet(attributeName, AnnotationAttributes.class);
 	}
 
+	/**
+	 * Get the annotation of type {@code annotationType} stored under the
+	 * specified {@code attributeName}.
+	 * @param attributeName the name of the attribute to get; never
+	 * {@code null} or empty
+	 * @param annotationType the expected annotation type; never {@code null}
+	 * @return the annotation
+	 * @throws IllegalArgumentException if the attribute does not exist or
+	 * if it is not of the expected type
+	 * @since 4.2
+	 */
+	public <A extends Annotation> A getAnnotation(String attributeName, Class<A> annotationType) {
+		return doGet(attributeName, annotationType);
+	}
+
 	/**
 	 * Get the array of {@link AnnotationAttributes} stored under the specified
 	 * {@code attributeName}.
 	 * <p>If the value stored under the specified {@code attributeName} is
 	 * an instance of {@code AnnotationAttributes}, it will be wrapped in
 	 * a single-element array before returning it.
+	 * <p>Note: if you expect an actual array of annotations, invoke
+	 * {@link #getAnnotationArray(String, Class)} instead.
 	 * @param attributeName the name of the attribute to get; never
 	 * {@code null} or empty
 	 * @return the array of {@code AnnotationAttributes}
@@ -231,6 +250,26 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 		return doGet(attributeName, AnnotationAttributes[].class);
 	}
 
+	/**
+	 * Get the array of type {@code annotationType} stored under the specified
+	 * {@code attributeName}.
+	 * <p>If the value stored under the specified {@code attributeName} is
+	 * an {@code Annotation}, it will be wrapped in a single-element array
+	 * before returning it.
+	 * @param attributeName the name of the attribute to get; never
+	 * {@code null} or empty
+	 * @param annotationType the expected annotation type; never {@code null}
+	 * @return the annotation array
+	 * @throws IllegalArgumentException if the attribute does not exist or
+	 * if it is not of the expected type
+	 * @since 4.2
+	 */
+	@SuppressWarnings("unchecked")
+	public <A extends Annotation> A[] getAnnotationArray(String attributeName, Class<A> annotationType) {
+		Object array = Array.newInstance(annotationType, 0);
+		return (A[]) doGet(attributeName, array.getClass());
+	}
+
 	/**
 	 * Get the value stored under the specified {@code attributeName},
 	 * ensuring that the value is of the {@code expectedType}.

spring-core/src/test/java/org/springframework/core/annotation/AnnotationAttributesTests.java

@@ -16,6 +16,9 @@
 
 package org.springframework.core.annotation;
 
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
@@ -32,10 +35,6 @@ import static org.junit.Assert.*;
  */
 public class AnnotationAttributesTests {
 
-	enum Color {
-		RED, WHITE, BLUE
-	}
-
 	private final AnnotationAttributes attributes = new AnnotationAttributes();
 
 	@Rule
@@ -72,7 +71,9 @@ public class AnnotationAttributesTests {
 	}
 
 	@Test
-	public void singleElementToSingleElementArrayConversionSupport() {
+	public void singleElementToSingleElementArrayConversionSupport() throws Exception {
+		Filter filter = FilteredClass.class.getAnnotation(Filter.class);
+
 		AnnotationAttributes nestedAttributes = new AnnotationAttributes();
 		nestedAttributes.put("name", "Dilbert");
 
@@ -80,15 +81,38 @@ public class AnnotationAttributesTests {
 		attributes.put("names", "Dogbert");
 		attributes.put("classes", Number.class);
 		attributes.put("nestedAttributes", nestedAttributes);
+		attributes.put("filters", filter);
 
 		// Get back arrays of single elements
 		assertThat(attributes.getStringArray("names"), equalTo(new String[] { "Dogbert" }));
 		assertThat(attributes.getClassArray("classes"), equalTo(new Class[] { Number.class }));
+
 		AnnotationAttributes[] array = attributes.getAnnotationArray("nestedAttributes");
 		assertNotNull(array);
-		assertTrue(array.getClass().isArray());
 		assertThat(array.length, is(1));
 		assertThat(array[0].getString("name"), equalTo("Dilbert"));
+
+		Filter[] filters = attributes.getAnnotationArray("filters", Filter.class);
+		assertNotNull(filters);
+		assertThat(filters.length, is(1));
+		assertThat(filters[0].pattern(), equalTo("foo"));
+	}
+
+	@Test
+	public void nestedAnnotations() throws Exception {
+		Filter filter = FilteredClass.class.getAnnotation(Filter.class);
+
+		attributes.put("filter", filter);
+		attributes.put("filters", new Filter[] { filter, filter });
+
+		Filter retrievedFilter = attributes.getAnnotation("filter", Filter.class);
+		assertThat(retrievedFilter, equalTo(filter));
+		assertThat(retrievedFilter.pattern(), equalTo("foo"));
+
+		Filter[] retrievedFilters = attributes.getAnnotationArray("filters", Filter.class);
+		assertNotNull(retrievedFilters);
+		assertEquals(2, retrievedFilters.length);
+		assertThat(retrievedFilters[1].pattern(), equalTo("foo"));
 	}
 
 	@Test
@@ -120,4 +144,17 @@ public class AnnotationAttributesTests {
 		attributes.getEnum("color");
 	}
 
+
+	enum Color {
+		RED, WHITE, BLUE
+	}
+
+	@Retention(RetentionPolicy.RUNTIME)
+	@interface Filter {
+		String pattern();
+	}
+
+	@Filter(pattern = "foo")
+	static class FilteredClass {
+	}
 }