Space: Apache BVal (https://cwiki.apache.org/confluence/display/BeanValidation)
Page: Obtaining a validator
(https://cwiki.apache.org/confluence/display/BeanValidation/Obtaining+a+validator)
Edited by Matt Benson:
---------------------------------------------------------------------
To obtain a validator, you must first create a ValidatorFactory. If there is
only one jsr303 implementation in your classpath, you can use:
{code:java}
ValidatorFactory vf = Validation.buildDefaultValidatorFactory();
{code}
to obtain the factory. If there are various implementations in the classpath,
or you want to be sure you are using the Apache one, you can use:
{code:java}
ValidatorFactory avf =
Validation.byProvider(ApacheValidationProvider.class).configure().buildValidatorFactory();
{code}
You should not instantiate more than one factory, as factory creation is a
costly process and the factory also acts as a constraint cache for the
validators.
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 are fine and should perform
equally well.
Below is an example that will create a singleton ValidatorFactory and will let
you obtain validators from it:
{code:java}
public enum MyValidatorFactory {
SINGLE_INSTANCE {
ValidatorFactory avf =
Validation.byProvider(ApacheValidationProvider.class).configure().buildValidatorFactory();
@Override
public Validator getValidator() {
return avf.getValidator();
}
};
public abstract Validator getValidator();
}
{code}
Using the above class, obtaining a validator just requires you to call:
{{MyValidatorFactory.SINGLE_INSTANCE.getValidator()}}
h3. Using Spring
If you are using Spring, you can easily inject validators in your beans. Simply
configure the factory in your applicationContext by adding:
{code:xml}
<!-- Validator bean -->
<bean id="validator"
class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean">
<property name="providerClass"
value="org.apache.bval.jsr303.ApacheValidationProvider" />
</bean>
{code}
And Spring will be able to inject Validators and the ValidatorFactory in your
beans.
h3. 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 the 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:
{code:xml}
<dependency>
<groupId>org.apache.bval</groupId>
<artifactId>bval-guice</artifactId>
<version>0.3-incubating</version>
</dependency>
{code}
Let's have a look at the features:
h5. Apache BVal bootstrapping
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_:
{code:java}
import com.google.inject.Guice;
import com.google.inject.Injector;
import org.apache.bval.guice.ValidationModule;
Injector injector = Guice.createInjector([...], new ValidationModule(), [...]);
{code}
h5. obtain _javax.validation.ConstraintValidator_ instances
Users can implement now _javax.validation.ConstraintValidator_ classes that
require _Dependency Injection_ by _Google Guice_:
{code:java}
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);
}
}
{code}
Don't forget to bind the {{MyExternalService}} class in the _Google Guice
Bincer_!!!
h5. 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:
{code:java}
import javax.validation.Validator;
public class MyValidatorClient {
@Inject
private Validator validator;
public void setValidator(Validator validator) {
this.validator = validator;
}
...
}
{code}
When obtaining {{MyValidatorClient}} instances from the _Injector_, the
{{javax.validation.Validator}} will be automagically bound.
h5. Intercept methods and validate method arguments
Taking advantage from the _Apache BVal_ extension to validate method arguments,
the {{bval-guice}} comes with an _AOP_ interceptor - automatically initialized
in the {{org.apache.bval.guice.ValidationModule}} - that makes easier the
methods arguments validation.
All users have to do is annotate interested methods with
{{org.apache.bval.guice.Validate}} annotation, then annotate arguments with
constraints, as follows below:
{code:java}
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 ...;
}
}
{code}
The {{org.apache.bval.guice.Validate}} supports 2 parameters:
* {{groups}} Class array, _empty_ by default, that marks the groups have to be
validated;
* {{validateReturnedValue}} flag, _false_ by default, that marks that if the
returned object by the method execution has to be validated.
h3. Using CDI
We recommend [MyFaces CODI|http://myfaces.apache.org/extensions/cdi/index.html].
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