DATACMNS-1357 - Use shared DefaultConversionService in ProxyProjectionFactory and ResultProcessor.

ProxyProjectionFactory and ResultProcessor require a DefaultConversionService to convert values for projection proxies and to post-process query method results. Creating instances of these types requires an instance of the conversion service which previously created a DefaultConversionService instance (along all converter registrations) upon ProxyProjection/ResultProcessor instantiation.

We now use the shared instance that is initialized once and shared across all ProxyProjection/ResultProcessor instances to reduce garbage and improve the CPU profile.

src/main/java/org/springframework/data/projection/ProxyProjectionFactory.java

@@ -41,6 +41,7 @@ import org.springframework.util.ConcurrentReferenceHashMap;
  *
  * @author Oliver Gierke
  * @author Christoph Strobl
+ * @author Mark Paluch
  * @see SpelAwareProxyProjectionFactory
  * @since 1.10
  */
@@ -60,7 +61,7 @@ class ProxyProjectionFactory implements ProjectionFactory, BeanClassLoaderAware
 		this.factories.add(MapAccessingMethodInterceptorFactory.INSTANCE);
 		this.factories.add(PropertyAccessingMethodInvokerFactory.INSTANCE);
 
-		this.conversionService = new DefaultConversionService();
+		this.conversionService = DefaultConversionService.getSharedInstance();
 	}
 
 	/*

src/main/java/org/springframework/data/repository/query/ResultProcessor.java

@@ -260,7 +260,7 @@ public class ResultProcessor {
 		 * @param factory must not be {@literal null}.
 		 */
 		ProjectingConverter(ReturnedType type, ProjectionFactory factory) {
-			this(type, factory, new DefaultConversionService());
+			this(type, factory, DefaultConversionService.getSharedInstance());
 		}
 
 		/**