Add additional AnnotationAttributes factory method

Add `createIfAnnotationPresent` method to `AnnotationAttributes` so that
a `MergedAnnotation` instance can be quickly converted to an
`AnnotationAttributes` Map.

The method is specifically designed to work with the `asMap` method
when the new API is not being used directly. For example:

	AnnotationAttributes attributes = mergedAnnotation.asMap(
		AnnotationAttributes::createIfAnnotationPresent);

See spring-projectsgh-21697

Author: philwebb

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

@@ -113,6 +113,22 @@ public AnnotationAttributes(Class<? extends Annotation> annotationType) {
 		this.displayName = annotationType.getName();
 	}
 
+	/**
+	 * Create a possibly already validated new, empty
+	 * {@link AnnotationAttributes} instance for the specified
+	 * {@code annotationType}.
+	 * @param annotationType the type of annotation represented by this
+	 * {@code AnnotationAttributes} instance; never {@code null}
+	 * @param validated if the attributes are considered already validated
+	 * @since 5.2
+	 */
+	AnnotationAttributes(Class<? extends Annotation> annotationType, boolean validated) {
+		Assert.notNull(annotationType, "'annotationType' must not be null");
+		this.annotationType = annotationType;
+		this.displayName = annotationType.getName();
+		this.validated = validated;
+	}
+
 	/**
 	 * Create a new, empty {@link AnnotationAttributes} instance for the
 	 * specified {@code annotationType}.
@@ -434,4 +450,17 @@ public static AnnotationAttributes fromMap(@Nullable Map<String, Object> map) {
 		return new AnnotationAttributes(map);
 	}
 
+	/**
+	 * Factory method used to create {@link AnnotationAttributes} only when the
+	 * specific annotation is present.
+	 * @param annotation the source annotation
+	 * @return a new {@link AnnotationAttributes} instance of {@code null}
+	 * @since 5.2
+	 * @see MergedAnnotation#asMap(java.util.function.Function,
+	 * org.springframework.core.annotation.MergedAnnotation.MapValues...)
+	 */
+	public static AnnotationAttributes createIfAnnotationPresent(MergedAnnotation<?> annotation) {
+		return annotation.isPresent() ? new AnnotationAttributes() : null;
+	}
+
 }

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

@@ -29,6 +29,8 @@
 
 import static org.hamcrest.CoreMatchers.*;
 import static org.junit.Assert.*;
+import static org.mockito.BDDMockito.given;
+import static org.mockito.Mockito.mock;
 
 /**
  * Unit tests for {@link AnnotationAttributes}.
@@ -221,6 +223,23 @@ public void getAliasedStringArrayWithImplicitAliases() {
 		aliases.stream().forEach(alias -> assertArrayEquals(new String[] {""}, attributes.getStringArray(alias)));
 	}
 
+	@Test
+	public void createIfAnnotationPresentWhenPresentReturnsAttributes() {
+		MergedAnnotation<?> annotation = mock(MergedAnnotation.class);
+		given(annotation.isPresent()).willReturn(true);
+		AnnotationAttributes attributes = AnnotationAttributes.createIfAnnotationPresent(
+				annotation);
+		assertThat(attributes, notNullValue());
+	}
+
+	@Test
+	public void createIfAnnotationPresentWhenNotPresentReturnsNull() {
+		MergedAnnotation<?> annotation = mock(MergedAnnotation.class);
+		AnnotationAttributes attributes = AnnotationAttributes.createIfAnnotationPresent(
+				annotation);
+		assertThat(attributes, nullValue());
+	}
+
 
 	enum Color {