Method Validation With Spring 3.1 and Hibernate Validator 4.2

JSR 303 and Hibernate Validator have been some awesome additions to the Java ecosystem, giving you a standard way to validate your domain model across application layers. Combined with the annotations of the Java Persistence API (JPA) you have some very nice tools at your disposal to ensure that only valid data enters your database.

However, one piece of missing functionality was the ability to also validate method calls. For example, wouldn't it be nice if you could use normal JSR 303 annotations to safeguard business layer calls as well?

Of course you can enforce constraints programmatically, e.g. prevent the passing of Null parameters. Spring for instance provides the org.springframework.util.Assert class. However, it would be desirable, if constraints placed on input parameters as well as return values were part of the method contract.

Enter Hibernate Validator 4.2, which was released in June of 2011. It provides now method validation and Gunnar Morling, one of the committers, has an excellent write-up on this on his blog at:

[url]http://musingsofaprogrammingaddict.blogspot.com/2011/01/method-validation-with-hibernate.html [/url]
Also, check out the Hibernate validator documentation regarding method validation. Gunnar Morling also provides some preliminary Spring support available at GitHub:

[url]https://github.com/gunnarmorling/methodvalidation-integration [/url]
But the news for Spring aficionados is getting even better - Direct support for Method Validation With Hibernate Validator is now available in the lastest Spring 3.1 release that went GA just two weeks ago.

Specifically Spring 3.1 provides the following support in regards to method validation:

org.springframework.validation.beanvalidation.MethodValidationInterceptor
org.springframework.validation.beanvalidation.MethodValidationPostProcessor
In order to get started, make sure that you are using Spring 3.1.0.RELEASE and that you have Hibernate Validator 4.2 in your classpath. That's all what you need to begin using JSR 303 annotations on the method level. For example, now you can annotate your methods using e.g.:

@Validatedpublic interface BusinessService {     
@NotNull String convertToUpperCase(@NotEmpty String input); 
} 

The @Validated Annotation indicates that the methods in the class are to be included for method validation. Keep in mind that you can specify your own annotation that will be enabling method level validation for the annotated class. Specify your own annotation by calling setValidatedAnnotationType on the MethodValidationPostProcessor.

However, placing the annotations themselves will not enforce the constraints 'automagically'. In fact Spring will be using AOP (Aspect Oriented Programming) Advices under the covers that delegate to Hibernate Validator. The easiest way to enable these advices is to declare a MethodValidationPostProcessor bean in your Spring application context as shown below.

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd   http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">    <context:component-scan base-package="com.hillert.spring.validation" />       <bean id="validator"      class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean"/>             <bean class="org.springframework.validation.beanvalidation.MethodValidationPostProcessor"/>       </beans>    

For more details, I have published a small project over at GitHub that illustrates method level validation using Hibernate Validator:

[url]https://github.com/ghillert/spring-hibernate-validator-sample [/url]
In order to get get started:

Clone the repository using $ git clone git://github.com/ghillert/spring-hibernate-validator-sample.git 
$ cd spring-hibernate-validator-sample
Build the sample using Maven $ mvn clean package
Run it with $ mvn exec:java 
The command-line based sample provides a simple String conversion service, that converts Strings to upper-case. You can insert those Strings from the command line. The Service layer will enforce the following constraints using method level Hibernate Validator annotations: