Do not enable cglib if spring.aop.proxy-target-class is configured

This commit makes sure to honour the `spring.aop.proxy-target-class`
property if set by the user. Previously, the
`MethodValidationPostProcessor` was always configured to use cglib,
regardless of the value of that property.

Closes gh-8869

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

@@ -24,10 +24,12 @@ import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnResource;
+import org.springframework.boot.bind.RelaxedPropertyResolver;
 import org.springframework.boot.validation.MessageInterpolatorFactory;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Role;
+import org.springframework.core.env.Environment;
 import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
 import org.springframework.validation.beanvalidation.MethodValidationPostProcessor;
 
@@ -56,11 +58,18 @@ public class ValidationAutoConfiguration {
 	@Bean
 	@ConditionalOnMissingBean
 	public static MethodValidationPostProcessor methodValidationPostProcessor(
-			Validator validator) {
+			Environment environment, Validator validator) {
 		MethodValidationPostProcessor processor = new MethodValidationPostProcessor();
-		processor.setProxyTargetClass(true);
+		processor.setProxyTargetClass(determineProxyTargetClass(environment));
 		processor.setValidator(validator);
 		return processor;
 	}
 
+	private static boolean determineProxyTargetClass(Environment environment) {
+		RelaxedPropertyResolver resolver = new RelaxedPropertyResolver(
+			environment, "spring.aop.");
+		Boolean value = resolver.getProperty("proxyTargetClass", Boolean.class);
+		return (value != null ? value : true);
+	}
+
 }

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

@@ -27,6 +27,7 @@ import org.junit.Test;
 import org.junit.rules.ExpectedException;
 
 import org.springframework.beans.DirectFieldAccessor;
+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;
@@ -75,6 +76,19 @@ public class ValidationAutoConfigurationTests {
 		service.doSomething(2);
 	}
 
+	@Test
+	public void validationCanBeConfiguredToUseJdkProxy() {
+		load(AnotherSampleServiceConfiguration.class, "spring.aop.proxy-target-class=false");
+		assertThat(this.context.getBeansOfType(Validator.class)).hasSize(1);
+		assertThat(this.context.getBeansOfType(DefaultAnotherSampleService.class))
+			.isEmpty();
+		AnotherSampleService service = this.context
+			.getBean(AnotherSampleService.class);
+		service.doSomething(42);
+		this.thrown.expect(ConstraintViolationException.class);
+		service.doSomething(2);
+	}
+
 	@Test
 	public void userDefinedMethodValidationPostProcessorTakesPrecedence() {
 		load(SampleConfiguration.class);
@@ -90,14 +104,15 @@ public class ValidationAutoConfigurationTests {
 						.getPropertyValue("validator"));
 	}
 
-	public void load(Class<?> config) {
-		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
+	public void load(Class<?> config, String... environment) {
+		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
+		EnvironmentTestUtils.addEnvironment(ctx, environment);
 		if (config != null) {
-			applicationContext.register(config);
+			ctx.register(config);
 		}
-		applicationContext.register(ValidationAutoConfiguration.class);
-		applicationContext.refresh();
-		this.context = applicationContext;
+		ctx.register(ValidationAutoConfiguration.class);
+		ctx.refresh();
+		this.context = ctx;
 	}
 
 	@Validated
@@ -123,6 +138,16 @@ public class ValidationAutoConfigurationTests {
 		}
 	}
 
+	@Configuration
+	static class AnotherSampleServiceConfiguration {
+
+		@Bean
+		public AnotherSampleService anotherSampleService() {
+			return new DefaultAnotherSampleService();
+		}
+
+	}
+
 	@Configuration
 	static class SampleConfiguration {