DATACMNS-1271 - Streamlined implementation of AnnotationBasedPersistentProperty to avoid NullPointerExceptions.

We now use the annotation cache's ….computeIfAbsent(…) to avoid inconsistencies between ….contains(…) and ….get(…) in multi-threaded scenarios.

src/main/java/org/springframework/data/mapping/model/AnnotationBasedPersistentProperty.java

@@ -39,6 +39,7 @@ import org.springframework.data.mapping.PersistentEntity;
 import org.springframework.data.mapping.PersistentProperty;
 import org.springframework.data.util.Lazy;
 import org.springframework.data.util.Optionals;
+import org.springframework.data.util.StreamUtils;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -229,22 +230,13 @@ public abstract class AnnotationBasedPersistentProperty<P extends PersistentProp
 	@SuppressWarnings("unchecked")
 	private <A extends Annotation> Optional<A> doFindAnnotation(Class<A> annotationType) {
 
-		if (annotationCache != null && annotationCache.containsKey(annotationType)) {
-			return (Optional<A>) annotationCache.get(annotationType);
-		}
+		return (Optional<A>) annotationCache.computeIfAbsent(annotationType, type -> {
 
-		return cacheAndReturn(annotationType, getAccessors()//
-				.flatMap(it -> {
-
-					A mergedAnnotation = AnnotatedElementUtils.findMergedAnnotation(it, annotationType);
-
-					if (mergedAnnotation == null) {
-						return Stream.empty();
-					}
-
-					return Stream.of(mergedAnnotation);
-				})//
-				.findFirst());
+			return getAccessors() //
+					.map(it -> AnnotatedElementUtils.findMergedAnnotation(it, type)) //
+					.flatMap(StreamUtils::fromNullable) //
+					.findFirst();
+		});
 	}
 
 	/*
@@ -260,18 +252,6 @@ public abstract class AnnotationBasedPersistentProperty<P extends PersistentProp
 		return annotation != null ? annotation : getOwner().findAnnotation(annotationType);
 	}
 
-	/**
-	 * Puts the given annotation into the local cache and returns it.
-	 *
-	 * @param annotation
-	 * @return
-	 */
-	private <A extends Annotation> Optional<A> cacheAndReturn(Class<? extends A> type, Optional<A> annotation) {
-
-		annotationCache.put(type, annotation);
-		return annotation;
-	}
-
 	/**
 	 * Returns whether the property carries the an annotation of the given type.
 	 *

src/main/java/org/springframework/data/util/StreamUtils.java

@@ -28,6 +28,7 @@ import java.util.stream.Collector;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.MultiValueMap;
 
@@ -95,4 +96,15 @@ public interface StreamUtils {
 			Function<T, V> valueFunction) {
 		return MultiValueMapCollector.of(keyFunction, valueFunction);
 	}
+
+	/**
+	 * Creates a new {@link Stream} for the given value returning an empty {@link Stream} if the value is {@literal null}.
+	 * 
+	 * @param source can be {@literal null}.
+	 * @return a new {@link Stream} for the given value returning an empty {@link Stream} if the value is {@literal null}.
+	 * @since 2.0.6
+	 */
+	public static <T> Stream<T> fromNullable(@Nullable T source) {
+		return source == null ? Stream.empty() : Stream.of(source);
+	}
 }