DATACMNS-1758 - Revert optimizations from DATACMNS-1698.

We ensure that each EntityCallback retrieval operates on its own List to not share the retrieved callback list with other threads.

src/main/java/org/springframework/data/mapping/callback/EntityCallbackDiscoverer.java

@@ -19,7 +19,6 @@ import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
@@ -188,7 +187,7 @@ class EntityCallbackDiscoverer {
 	private Collection<EntityCallback<?>> retrieveEntityCallbacks(ResolvableType entityType, ResolvableType callbackType,
 			@Nullable CallbackRetriever retriever) {
 
-		List<EntityCallback<?>> allCallbacks = null;
+		List<EntityCallback<?>> allCallbacks = new ArrayList<>();
 		Set<EntityCallback<?>> callbacks;
 		Set<String> callbackBeans;
 
@@ -199,9 +198,8 @@ class EntityCallbackDiscoverer {
 
 		for (EntityCallback<?> callback : callbacks) {
 			if (supportsEvent(callback, entityType, callbackType)) {
-
-				if (allCallbacks == null) {
-					allCallbacks = new ArrayList<>();
+				if (retriever != null) {
+					retriever.getEntityCallbacks().add(callback);
 				}
 				allCallbacks.add(callback);
 			}
@@ -214,9 +212,7 @@ class EntityCallbackDiscoverer {
 					Class<?> callbackImplType = beanFactory.getType(callbackBeanName);
 					if (callbackImplType == null || supportsEvent(callbackImplType, entityType)) {
 						EntityCallback<?> callback = beanFactory.getBean(callbackBeanName, EntityCallback.class);
-
-						if ((allCallbacks == null || !allCallbacks.contains(callback))
-								&& supportsEvent(callback, entityType, callbackType)) {
+						if (!allCallbacks.contains(callback) && supportsEvent(callback, entityType, callbackType)) {
 							if (retriever != null) {
 								if (beanFactory.isSingleton(callbackBeanName)) {
 									retriever.entityCallbacks.add(callback);
@@ -224,10 +220,6 @@ class EntityCallbackDiscoverer {
 									retriever.entityCallbackBeans.add(callbackBeanName);
 								}
 							}
-
-							if (allCallbacks == null) {
-								allCallbacks = new ArrayList<>();
-							}
 							allCallbacks.add(callback);
 						}
 					}
@@ -238,10 +230,6 @@ class EntityCallbackDiscoverer {
 			}
 		}
 
-		if (allCallbacks == null) {
-			return Collections.emptyList();
-		}
-
 		AnnotationAwareOrderComparator.sort(allCallbacks);
 
 		if (retriever != null && retriever.entityCallbackBeans.isEmpty()) {
@@ -369,8 +357,6 @@ class EntityCallbackDiscoverer {
 
 		private final Set<EntityCallback<?>> entityCallbacks = new LinkedHashSet<>();
 
-		private final List<EntityCallback<?>> cachedEntityCallbacks = new ArrayList<>();
-
 		private final Set<String> entityCallbackBeans = new LinkedHashSet<>();
 
 		private final boolean preFiltered;
@@ -381,22 +367,6 @@ class EntityCallbackDiscoverer {
 
 		Collection<EntityCallback<?>> getEntityCallbacks() {
 
-			if (this.entityCallbackBeans.isEmpty()) {
-
-				if (cachedEntityCallbacks.size() != entityCallbacks.size()) {
-
-					List<EntityCallback<?>> entityCallbacks = new ArrayList<>(this.entityCallbacks);
-					AnnotationAwareOrderComparator.sort(entityCallbacks);
-
-					synchronized (cachedEntityCallbacks) {
-						cachedEntityCallbacks.clear();
-						cachedEntityCallbacks.addAll(entityCallbacks);
-					}
-				}
-
-				return cachedEntityCallbacks;
-			}
-
 			List<EntityCallback<?>> allCallbacks = new ArrayList<>(
 					this.entityCallbacks.size() + this.entityCallbackBeans.size());
 			allCallbacks.addAll(this.entityCallbacks);