HV-1772 Allow overriding MessageInterpolator when config is reused

engine/src/main/java/org/hibernate/validator/internal/engine/AbstractConfigurationImpl.java

@@ -409,6 +409,9 @@ public T externalClassLoader(ClassLoader externalClassLoader) {
 		Contracts.assertNotNull( externalClassLoader, MESSAGES.parameterMustNotBeNull( "externalClassLoader" ) );
 		this.externalClassLoader = externalClassLoader;
 
+		// we need to reset the messageInterpolator field as it might vary depending on the class loader
+		this.messageInterpolator = null;
+
 		return thisAsT();
 	}
 
@@ -468,15 +471,13 @@ public final boolean isIgnoreXmlConfiguration() {
 
 	@Override
 	public final MessageInterpolator getMessageInterpolator() {
+		// apply explicitly given MI, otherwise use default one
+		MessageInterpolator selectedInterpolator = validationBootstrapParameters.getMessageInterpolator();
+		if ( selectedInterpolator != null ) {
+			return selectedInterpolator;
+		}
 		if ( messageInterpolator == null ) {
-			// apply explicitly given MI, otherwise use default one
-			MessageInterpolator interpolator = validationBootstrapParameters.getMessageInterpolator();
-			if ( interpolator != null ) {
-				messageInterpolator = interpolator;
-			}
-			else {
-				messageInterpolator = getDefaultMessageInterpolatorConfiguredWithClassLoader();
-			}
+			messageInterpolator = getDefaultMessageInterpolatorConfiguredWithClassLoader();
 		}
 
 		return messageInterpolator;

engine/src/test/java/org/hibernate/validator/test/internal/bootstrap/ConfigurationReuseHibernateValidatorTest.java

@@ -0,0 +1,59 @@
+/*
+ * Hibernate Validator, declare and validate application constraints
+ *
+ * License: Apache License, Version 2.0
+ * See the license.txt file in the root directory or <http://www.apache.org/licenses/LICENSE-2.0>.
+ */
+package org.hibernate.validator.test.internal.bootstrap;
+
+import static org.testng.Assert.assertSame;
+
+import java.util.Locale;
+
+import jakarta.validation.Configuration;
+import jakarta.validation.MessageInterpolator;
+import jakarta.validation.Validation;
+import jakarta.validation.ValidatorFactory;
+
+import org.testng.annotations.Test;
+
+/**
+ * @author Steven Walters
+ * @author Guillaume Smet
+ */
+public class ConfigurationReuseHibernateValidatorTest {
+
+	public static class MessageInterpolatorImpl implements MessageInterpolator {
+
+		private final String prefix;
+
+		public MessageInterpolatorImpl(String prefix) {
+			this.prefix = prefix;
+		}
+
+		@Override
+		public String interpolate(String messageTemplate, Context context) {
+			return prefix + ": " + messageTemplate;
+		}
+
+		@Override
+		public String interpolate(String messageTemplate, Context context, Locale locale) {
+			return prefix + ": " + messageTemplate + locale.toLanguageTag();
+		}
+
+		public String toString() {
+			return getClass().getSimpleName() + prefix;
+		}
+	}
+
+	@Test
+	public void testMessageInterpolatorChange() {
+		Configuration<?> config = Validation.byDefaultProvider().configure();
+		MessageInterpolator interpolator1 = new MessageInterpolatorImpl( "One" );
+		MessageInterpolator interpolator2 = new MessageInterpolatorImpl( "Two" );
+		ValidatorFactory factory1 = config.messageInterpolator( interpolator1 ).buildValidatorFactory();
+		ValidatorFactory factory2 = config.messageInterpolator( interpolator2 ).buildValidatorFactory();
+		assertSame( factory1.getMessageInterpolator(), interpolator1 );
+		assertSame( factory2.getMessageInterpolator(), interpolator2 );
+	}
+}