Auto-configure validation constraints on bean methods

This commit auto-configures `MethodValidationPostProcessor` if necessary
when a JSR-303 validator implementation is detected on the classpath.

Closes gh-6228

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

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2012-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.validation;
+
+import javax.validation.Validator;
+
+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.context.annotation.Bean;
+import org.springframework.validation.beanvalidation.MethodValidationPostProcessor;
+
+/**
+ * {@link EnableAutoConfiguration Auto-configuration} to configure the validation
+ * infrastructure.
+ *
+ * @author Stephane Nicoll
+ * @since 1.5.0
+ */
+@ConditionalOnClass({ Validator.class })
+public class ValidationAutoConfiguration {
+
+	@Bean
+	@ConditionalOnResource(resources = "META-INF/services/javax.validation.spi.ValidationProvider")
+	@ConditionalOnMissingBean
+	public MethodValidationPostProcessor methodValidationPostProcessor() {
+		return new MethodValidationPostProcessor();
+	}
+
+}

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

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Auto-configuration for (JSR-303) Validation.
+ */
+package org.springframework.boot.autoconfigure.validation;

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

@@ -0,0 +1,99 @@
+/*
+ * Copyright 2012-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.validation;
+
+import javax.validation.ConstraintViolationException;
+import javax.validation.constraints.Size;
+
+import org.junit.After;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.validation.annotation.Validated;
+import org.springframework.validation.beanvalidation.MethodValidationPostProcessor;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ValidationAutoConfiguration}.
+ *
+ * @author Stephane Nicoll
+ */
+public class ValidationAutoConfigurationTests {
+
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
+	private AnnotationConfigApplicationContext context;
+
+	@After
+	public void close() {
+		if (this.context != null) {
+			this.context.close();
+		}
+	}
+
+	@Test
+	public void validationIsEnabled() {
+		load(SampleService.class);
+		SampleService service = this.context.getBean(SampleService.class);
+		service.doSomething("Valid");
+		this.thrown.expect(ConstraintViolationException.class);
+		service.doSomething("KO");
+	}
+
+	@Test
+	public void userDefinedMethodValidationPostProcessorTakesPrecedence() {
+		load(SampleConfiguration.class);
+		assertThat(this.context.getBean(MethodValidationPostProcessor.class))
+				.isSameAs(this.context.getBean("testMethodValidationPostProcessor"));
+		assertThat(this.context.getBeansOfType(MethodValidationPostProcessor.class)).hasSize(1);
+	}
+
+	public void load(Class<?> config) {
+		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
+		if (config != null) {
+			applicationContext.register(config);
+		}
+		applicationContext.register(ValidationAutoConfiguration.class);
+		applicationContext.refresh();
+		this.context = applicationContext;
+	}
+
+	@Validated
+	static class SampleService {
+
+		public void doSomething(@Size(min = 3, max = 10) String name) {
+
+		}
+	}
+
+	@Configuration
+	static class SampleConfiguration {
+
+		@Bean
+		public MethodValidationPostProcessor testMethodValidationPostProcessor() {
+			return new MethodValidationPostProcessor();
+		}
+
+	}
+
+}

spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -4616,6 +4616,34 @@ Lastly, the most extreme (and rarely used) option is to create your own
 
 
 
+[[boot-features-validation]]
+== Validation
+The method validation feature supported by Bean Validation 1.1 is automatically enabled
+as long as a JSR-303 implementation (e.g. Hibernate validator) is on the classpath. This
+allows bean methods to be annotated with `javax.validation` constraints on their
+parameters and/or on their return value. Target classes with such annotated methods need
+to be annotated with the `@Validated` annotation at the type level for their methods to
+be searched for inline constraint annotations.
+
+For instance, the following service triggers the validation of the first argument, making
+sure its size is between 8 and 10
+
+[source,java,indent=0]
+----
+	@Service
+	@Validated
+	public class MyBean {
+
+		public Archive findByCodeAndAuthor(@Size(min = 8, max = 10) String code,
+				Author author) {
+			...
+		}
+
+	}
+----
+
+
+
 [[boot-features-email]]
 == Sending email
 The Spring Framework provides an easy abstraction for sending email using the