Revise PartTree query caching.

See #3588
Original pull request: #3653

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/JpqlQueryBuilder.java

@@ -450,7 +450,7 @@ default Select instantiate(Class<?> resultType, Collection<JpqlQueryBuilder.Path
 		/**
 		 * Select a single attribute.
 		 *
-		 * @param name
+		 * @param path
 		 * @return
 		 */
 		default Select select(JpqlQueryBuilder.PathExpression path) {

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/PartTreeJpaQuery.java

@@ -279,12 +279,8 @@ private Query restrictMaxResultsIfNecessary(Query query, @Nullable ScrollPositio
 
 		protected JpqlQueryCreator createCreator(Sort sort, JpaParametersParameterAccessor accessor) {
 
-			JpqlQueryCreator jpqlQueryCreator;
-			synchronized (cache) {
-				jpqlQueryCreator = cache.get(sort, accessor); // this caching thingy is broken due to IS NULL rendering for
-																											// simple properties
-			}
-
+			JpqlQueryCreator jpqlQueryCreator = cache.get(sort, accessor); // this caching thingy is broken due to IS NULL
+																																			// rendering for
 			if (jpqlQueryCreator != null) {
 				return jpqlQueryCreator;
 			}
@@ -307,9 +303,7 @@ protected JpqlQueryCreator createCreator(Sort sort, JpaParametersParameterAccess
 				return creator;
 			}
 
-			synchronized (cache) {
-				cache.put(sort, accessor, creator);
-			}
+			cache.put(sort, accessor, creator);
 
 			return creator;
 		}
@@ -377,13 +371,12 @@ private Sort getDynamicSort(JpaParametersParameterAccessor accessor) {
 	 */
 	private class CountQueryPreparer extends QueryPreparer {
 
-		private volatile JpqlQueryCreator cached;
+		private final PartTreeQueryCache cache = new PartTreeQueryCache();
 
 		@Override
 		protected JpqlQueryCreator createCreator(Sort sort, JpaParametersParameterAccessor accessor) {
 
-			JpqlQueryCreator cached = this.cached;
-
+			JpqlQueryCreator cached = cache.get(Sort.unsorted(), accessor);
 			if (cached != null) {
 				return cached;
 			}
@@ -393,7 +386,9 @@ protected JpqlQueryCreator createCreator(Sort sort, JpaParametersParameterAccess
 					getQueryMethod().getResultProcessor().getReturnedType(), provider, templates, em);
 
 			if (!accessor.getParameters().hasDynamicProjection()) {
-				return this.cached = new CacheableJpqlCountQueryCreator(creator);
+				cached = new CacheableJpqlCountQueryCreator(creator);
+				cache.put(Sort.unsorted(), accessor, cached);
+				return cached;
 			}
 
 			return creator;

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/PartTreeQueryCache.java

@@ -16,6 +16,7 @@
 package org.springframework.data.jpa.repository.query;
 
 import java.util.BitSet;
+import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
@@ -31,12 +32,12 @@
  */
 class PartTreeQueryCache {
 
-	private final Map<CacheKey, JpqlQueryCreator> cache = new LinkedHashMap<>() {
+	private final Map<CacheKey, JpqlQueryCreator> cache = Collections.synchronizedMap(new LinkedHashMap<>() {
 		@Override
 		protected boolean removeEldestEntry(Map.Entry<CacheKey, JpqlQueryCreator> eldest) {
 			return size() > 256;
 		}
-	};
+	});
 
 	@Nullable
 	JpqlQueryCreator get(Sort sort, JpaParametersParameterAccessor accessor) {