Stop auto-config of MethodValidationPP triggering early init

Previously, if a user's configuration class provided a custom
Validator bean, that configuration class would be initialized very
early so that the Validator could be used to create the
auto-configured MethodValidationPostProcessor. This early
initialization could problems as it may prevent any of the
configuration class's dependencies from being post-processed.

This commit updates the injection of the Validator bean to be lazy,
thereby preventing the creation of the auto-configured
MethodValidationPostProcessor from triggering early initialization.

Closes gh-9416

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/validation/ValidationAutoConfiguration.java

@@ -29,6 +29,7 @@ import org.springframework.boot.validation.MessageInterpolatorFactory;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
+import org.springframework.context.annotation.Lazy;
 import org.springframework.context.annotation.Role;
 import org.springframework.core.env.Environment;
 import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
@@ -60,7 +61,7 @@ public class ValidationAutoConfiguration {
 	@Bean
 	@ConditionalOnMissingBean
 	public static MethodValidationPostProcessor methodValidationPostProcessor(
-			Environment environment, Validator validator) {
+			Environment environment, @Lazy Validator validator) {
 		MethodValidationPostProcessor processor = new MethodValidationPostProcessor();
 		processor.setProxyTargetClass(determineProxyTargetClass(environment));
 		processor.setValidator(validator);

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/validation/ValidationAutoConfigurationTests.java

@@ -16,6 +16,9 @@
 
 package org.springframework.boot.autoconfigure.validation;
 
+import java.util.HashSet;
+import java.util.Set;
+
 import javax.validation.ConstraintViolationException;
 import javax.validation.Validator;
 import javax.validation.constraints.Min;
@@ -27,12 +30,15 @@ import org.junit.Test;
 import org.junit.rules.ExpectedException;
 
 import org.springframework.beans.DirectFieldAccessor;
+import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.boot.autoconfigure.validation.ValidationAutoConfigurationTests.CustomValidatorConfiguration.TestBeanPostProcessor;
 import org.springframework.boot.test.util.EnvironmentTestUtils;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Primary;
 import org.springframework.validation.annotation.Validated;
+import org.springframework.validation.beanvalidation.CustomValidatorBean;
 import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
 import org.springframework.validation.beanvalidation.MethodValidationPostProcessor;
 import org.springframework.validation.beanvalidation.OptionalValidatorFactoryBean;
@@ -198,6 +204,13 @@ public class ValidationAutoConfigurationTests {
 						.getPropertyValue("validator"));
 	}
 
+	@Test
+	public void methodValidationPostProcessorValidatorDependencyDoesNotTriggerEarlyInitialization() {
+		load(CustomValidatorConfiguration.class);
+		assertThat(this.context.getBean(TestBeanPostProcessor.class).postProcessed)
+				.contains("someService");
+	}
+
 	private boolean isPrimaryBean(String beanName) {
 		return this.context.getBeanDefinition(beanName).isPrimary();
 	}
@@ -322,4 +335,53 @@ public class ValidationAutoConfigurationTests {
 
 	}
 
+	@Configuration
+	static class CustomValidatorConfiguration {
+
+		CustomValidatorConfiguration(SomeService someService) {
+
+		}
+
+		@Bean
+		Validator customValidator() {
+			return new CustomValidatorBean();
+		}
+
+		@Bean
+		static TestBeanPostProcessor testBeanPostProcessor() {
+			return new TestBeanPostProcessor();
+		}
+
+		@Configuration
+		static class SomeServiceConfiguration {
+
+			@Bean
+			public SomeService someService() {
+				return new SomeService();
+			}
+
+		}
+
+		static class SomeService {
+
+		}
+
+		static class TestBeanPostProcessor implements BeanPostProcessor {
+
+			private Set<String> postProcessed = new HashSet<String>();
+
+			@Override
+			public Object postProcessAfterInitialization(Object bean, String name) {
+				this.postProcessed.add(name);
+				return bean;
+			}
+
+			@Override
+			public Object postProcessBeforeInitialization(Object bean, String name) {
+				return bean;
+			}
+
+		}
+	}
+
 }