Apache BVal

To obtain a Validator, you must first create a ValidatorFactory. If there is only one Bean Validation implementation in your classpath, you can use:

    ValidatorFactory vf = Validation.buildDefaultValidatorFactory();

to obtain the factory. If there are various implementations in the classpath, or you want to be sure you are using Apache BVal, you can use:

    ValidatorFactory avf =
        Validation.byProvider(ApacheValidationProvider.class).configure().buildValidatorFactory();

You should usually not instantiate more than one factory; factory creation is a costly process. Also, the factory also acts as a cache for the available validation constraints.

Once you have a ValidatorFactory, obtaining a validator just requires you to call ValidatorFactory#getValidator(). The validator implementation is thread-safe, so you can choose to re-use a single instance of it in all your code or create validators on demand: both options should perform equally well.

Below is an example that will create a singleton ValidatorFactory and will let you obtain Validators from it:

    public enum MyValidatorFactory  {

        SINGLE_INSTANCE  {

            ValidatorFactory avf =
                Validation.byProvider(ApacheValidationProvider.class).configure().buildValidatorFactory();

            @Override
            public Validator getValidator()  {
                return avf.getValidator();
            }

        };

        public abstract Validator getValidator(); 
    }

Using the above class, obtaining a Validator just requires you to call:

    MyValidatorFactory.SINGLE_INSTANCE.getValidator()

Using The Spring Framework ¶

If you are using Spring, you can easily inject Validators into your beans. Simply configure the factory in your ApplicationContext by adding:

    <!-- Validator bean -->
    <bean id="validator"
        class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean">
        <property name="providerClass"
            value="org.apache.bval.jsr303.ApacheValidationProvider" />
    </bean>

And Spring will be able to inject Validators and the ValidatorFactory into your beans.

Using Google Guice¶

Apache BVal provides the bval-guice module that simplifies integration with Google Guice. That module has multiple purposes, such:

bootstrap Apache BVal using Google Guice;
obtain javax.validation.ConstraintValidator instances using the Google Guice Injector to easily support DI;
easily inject the javax.validation.Validator reference into components that require it;
easily intercept methods and validate method arguments.

First of all, users have to add the bval-guice module in the classpath; Apache Maven users can easily include it just by adding the following dependency in the POM:

    <dependency>
      <groupId>org.apache.bval</groupId>
      <artifactId>bval-guice</artifactId>
      <version>0.3-incubating</version>
    </dependency>

Let's have a look at the features:

Bootstrapping Apache BVal

Simply, the org.apache.bval.guice.ValidationModule is the Google Guice module that bootstraps Apache BVal. All users have to do is add this module when creating the Google Guice Injector:

    import com.google.inject.Guice;
    import com.google.inject.Injector;

    import org.apache.bval.guice.ValidationModule;

    Injector injector = Guice.createInjector([...](....html),
        new ValidationModule(), [...]
    );

Obtain `javax.validation.ConstraintValidator` instances

Users can now implement javax.validation.ConstraintValidator classes that require Dependency Injection by Google Guice:

    import javax.validation.ConstraintValidator;

    public class MyCustomValidator implements ConstraintValidator<MyAssert, MyType>  {

        private final MyExternalService service;

        @Inject
        public MyCustomValidator(MyExternalService service)  {
    	this.service = service;
        }

        public void initialize(MyAssert annotation)  {
    	// do something
        }

        public boolean isValid(MyType value, ConstraintValidatorContext context)  {
            return value == null || this.service.doSomething(value);
        }
    }

Don't forget to bind the MyExternalService class in the Google Guice Binder!!!

Inject the `javax.validation.Validator` reference

Clients can easily inject javax.validation.Validator instances into their custom components just marking it using the Google Guice @Inject annotation:

    import javax.validation.Validator;

    public class MyValidatorClient  {

        @Inject
        private Validator validator;

        public void setValidator(Validator validator)  {
	    this.validator = validator;
        }

        // ...

    }

When obtaining MyValidatorClient instances from the Injector, the javax.validation.Validator will be automagically bound.

Intercept methods and validate method arguments

Taking advantage of the Apache BVal extension to validate method arguments, the bval-guice module comes with an AOP interceptor, automatically initialized in the org.apache.bval.guice.ValidationModule, that facilitates the validation of method arguments.

All users have to do is annotate interested methods with org.apache.bval.guice.Validate annotation, then annotate arguments with constraints, as follows below:

    import javax.validation.constraints.NotNull;
    import javax.validation.constraints.Size;
    
    import org.apache.bval.guice.Validate;
    
    public class MyService  {
    
        @Validate(
    	    groups =  { MyGroup.class },
    	    validateReturnedValue = true
        )
        public Country insertCountry(@NotNull(groups =  { MyGroup.class })
    	    String name,
    	    @NotNull(groups =  { MyGroup.class })
    	    @Size(max = 2, groups =  { MyGroup.class, MyOtherGroup.class })
    	    String iso2Code,
    	    @NotNull(groups =  { MyGroup.class })
    	    @Size(max = 3, groups =  { MyGroup.class, MyOtherGroup.class })
    	    String iso3Code)  {

    	    return ...;
        }

    }

The bval-guice @Validate annotation supports 2 values:

groups Class array, {} by default, that specifies the groups to be validated;
validateReturnedValue flag, false by default, indicating whether the method's return value should be validated.

Using CDI¶

Bean Validation integration with CDI is provided by:

The Bean Validation integration module of MyFaces CODI
Seam Validation Module

Using The Spring Framework¶