DATACMNS-1366 - Performance improvements in mapping subsystem

We now use a presized HashMap and Weak references in BasicPersistentEntity to improve memory and CPU profile and and avoid unmodifiable collection creation in BasicPersistentEntity.iterator(). Refactored ClassTypeInformation.from(…) lambda to method reference and predefined collection size for the cache. Reduced object instantiations during TypeDiscoverer.equals(…) by checking for type variable map emptiness to avoid Map iterator creation in Map.equals(…).

Original pull request: #305.

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

@@ -105,7 +105,7 @@ public class BasicPersistentEntity<T, P extends PersistentProperty<P>> implement
 		this.constructor = PreferredConstructorDiscoverer.discover(this);
 		this.associations = comparator == null ? new HashSet<>() : new TreeSet<>(new AssociationComparator<>(comparator));
 
-		this.propertyCache = new HashMap<>();
+		this.propertyCache = new HashMap<>(16, 1f);
 		this.annotationCache = new ConcurrentReferenceHashMap<>(16, ReferenceType.WEAK);
 		this.propertyAnnotationCache = CollectionUtils
 				.toMultiValueMap(new ConcurrentReferenceHashMap<>(16, ReferenceType.WEAK));
@@ -507,7 +507,21 @@ public class BasicPersistentEntity<T, P extends PersistentProperty<P>> implement
 	 */
 	@Override
 	public Iterator<P> iterator() {
-		return Collections.unmodifiableList(properties).iterator();
+
+		Iterator<P> iterator = properties.iterator();
+
+		return new Iterator<P>() {
+
+			@Override
+			public boolean hasNext() {
+				return iterator.hasNext();
+			}
+
+			@Override
+			public P next() {
+				return iterator.next();
+			}
+		};
 	}
 
 	protected EvaluationContext getEvaluationContext(Object rootObject) {