HV-1480 Avoid creating a list in the common case when we only have the

default violation

Also optimize a bit the concatenation of the default violation and the
custom ones to avoid creating a list too small and resize it each time.

Author: gsmet

engine/src/main/java/org/hibernate/validator/internal/engine/constraintvalidation/ConstraintValidatorContextImpl.java

@@ -6,8 +6,6 @@
  */
 package org.hibernate.validator.internal.engine.constraintvalidation;
 
-import static org.hibernate.validator.internal.util.CollectionHelper.newArrayList;
-
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
@@ -30,6 +28,7 @@
 
 import org.hibernate.validator.constraintvalidation.HibernateConstraintValidatorContext;
 import org.hibernate.validator.internal.engine.path.PathImpl;
+import org.hibernate.validator.internal.util.CollectionHelper;
 import org.hibernate.validator.internal.util.Contracts;
 import org.hibernate.validator.internal.util.logging.Log;
 import org.hibernate.validator.internal.util.logging.LoggerFactory;
@@ -47,9 +46,9 @@ public class ConstraintValidatorContextImpl implements HibernateConstraintValida
 	private Map<String, Object> expressionVariables;
 	private final List<String> methodParameterNames;
 	private final ClockProvider clockProvider;
-	private final List<ConstraintViolationCreationContext> constraintViolationCreationContexts = newArrayList( 3 );
 	private final PathImpl basePath;
 	private final ConstraintDescriptor<?> constraintDescriptor;
+	private List<ConstraintViolationCreationContext> constraintViolationCreationContexts;
 	private boolean defaultDisabled;
 	private Object dynamicPayload;
 
@@ -129,25 +128,34 @@ public final ConstraintDescriptor<?> getConstraintDescriptor() {
 	}
 
 	public final List<ConstraintViolationCreationContext> getConstraintViolationCreationContexts() {
-		if ( defaultDisabled && constraintViolationCreationContexts.size() == 0 ) {
-			throw log.getAtLeastOneCustomMessageMustBeCreatedException();
+		if ( defaultDisabled ) {
+			if ( constraintViolationCreationContexts == null || constraintViolationCreationContexts.size() == 0 ) {
+				throw log.getAtLeastOneCustomMessageMustBeCreatedException();
+			}
+
+			return CollectionHelper.toImmutableList( constraintViolationCreationContexts );
 		}
 
-		List<ConstraintViolationCreationContext> returnedConstraintViolationCreationContexts = new ArrayList<>(
-				constraintViolationCreationContexts
-		);
-		if ( !defaultDisabled ) {
-			returnedConstraintViolationCreationContexts.add(
-					new ConstraintViolationCreationContext(
-							getDefaultConstraintMessageTemplate(),
-							basePath,
-							messageParameters != null ? new HashMap<>( messageParameters ) : Collections.emptyMap(),
-							expressionVariables != null ? new HashMap<>( expressionVariables ) : Collections.emptyMap(),
-							dynamicPayload
-					)
-			);
+		if ( constraintViolationCreationContexts == null || constraintViolationCreationContexts.size() == 0 ) {
+			return Collections.singletonList( getDefaultConstraintViolationCreationContext() );
 		}
-		return returnedConstraintViolationCreationContexts;
+
+		List<ConstraintViolationCreationContext> returnedConstraintViolationCreationContexts =
+				new ArrayList<>( constraintViolationCreationContexts.size() + 1 );
+		returnedConstraintViolationCreationContexts.addAll( constraintViolationCreationContexts );
+		returnedConstraintViolationCreationContexts.add( getDefaultConstraintViolationCreationContext() );
+
+		return CollectionHelper.toImmutableList( returnedConstraintViolationCreationContexts );
+	}
+
+	private ConstraintViolationCreationContext getDefaultConstraintViolationCreationContext() {
+		return new ConstraintViolationCreationContext(
+				getDefaultConstraintMessageTemplate(),
+				basePath,
+				messageParameters != null ? new HashMap<>( messageParameters ) : Collections.emptyMap(),
+				expressionVariables != null ? new HashMap<>( expressionVariables ) : Collections.emptyMap(),
+				dynamicPayload
+		);
 	}
 
 	public List<String> getMethodParameterNames() {
@@ -164,6 +172,9 @@ protected NodeBuilderBase(String template, PathImpl path) {
 		}
 
 		public ConstraintValidatorContext addConstraintViolation() {
+			if ( constraintViolationCreationContexts == null ) {
+				constraintViolationCreationContexts = CollectionHelper.newArrayList( 3 );
+			}
 			constraintViolationCreationContexts.add(
 					new ConstraintViolationCreationContext(
 							messageTemplate,