Chapter 8. Bootstrapping

In Section 2.2.1, “Obtaining a Validator instance” you already saw one way for creating a Validator instance - via Validation#buildDefaultValidatorFactory(). In this chapter you will learn how to use the other methods in javax.validation.Validation in order to bootstrap specifically configured validators.

8.1. Retrieving `ValidatorFactory` and `Validator`

You obtain a Validator by retrieving a ValidatorFactory via one of the static methods on javax.validation.Validation and calling getValidator() on the factory instance.

Example 8.1, “Bootstrapping default ValidatorFactory and Validator” shows how to obtain a validator from the default validator factory:

Example 8.1. Bootstrapping default ValidatorFactory and Validator

ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
Validator validator = factory.getValidator();

Tip

The generated ValidatorFactory and Validator instances are thread-safe and can be cached. As Hibernate Validator uses the factory as context for caching constraint metadata it is recommended to work with one factory instance within an application.

Bean Validation supports working with several providers such as Hibernate Validator within one application. If more than one provider is present on the classpath, it is not guaranteed which one is chosen when creating a factory via buildDefaultValidatorFactory().

In this case you can explicitly specify the provider to use via Validation#byProvider(), passing the provider’s ValidationProvider class as shown in Example 8.2, “Bootstrapping ValidatorFactory and Validator using a specific provider”.

Example 8.2. Bootstrapping ValidatorFactory and Validator using a specific provider

ValidatorFactory validatorFactory = Validation.byProvider( HibernateValidator.class )
		.configure()
		.buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

Note that the configuration object returned by configure() allows to specifically customize the factory before calling buildValidatorFactory(). The available options are discussed later in this chapter.

Example 8.3. Retrieving the default ValidatorFactory for configuration

ValidatorFactory validatorFactory = Validation.byDefaultProvider()
		.configure()
		.buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

Note

If a ValidatorFactory instance is no longer in use, it should be disposed by calling ValidatorFactory#close(). This will free any resources possibly allocated by the factory.

8.1.1. `ValidationProviderResolver`

By default, available Bean Validation providers are discovered using the Java Service Provider mechanism.

For that purpose, each provider includes the file META- INF/services/javax.validation.spi.ValidationProvider, containing the fully qualified classname of its ValidationProvider implementation. In the case of Hibernate Validator this is org.hibernate.validator.HibernateValidator.

Depending on your environment and its classloading specifics, provider discovery via the Java’s service loader mechanism might not work. In this case you can plug in a custom ValidationProviderResolver implementation which performs the provider retrieval. An example is OSGi, where you could implement a provider resolver which uses OSGi services for provider discovery.

To use a custom provider resolver pass it via providerResolver() as shown shown in Example 8.4, “Using a custom ValidationProviderResolver”.

Example 8.4. Using a custom ValidationProviderResolver

package org.hibernate.validator.referenceguide.chapter08;

public class OsgiServiceDiscoverer implements ValidationProviderResolver {

	@Override
	public List<ValidationProvider<?>> getValidationProviders() {
		//...
	}
}

ValidatorFactory validatorFactory = Validation.byDefaultProvider()
		.providerResolver( new OsgiServiceDiscoverer() )
		.configure()
		.buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

8.2. Configuring a `ValidatorFactory`

By default validator factories retrieved from Validation and any validators they create are configured as per the XML descriptor META-INF/validation.xml (see Chapter 7, Configuring via XML), if present.

If you want to disable the XML based configuration, you can do so by invoking Configuration#ignoreXmlConfiguration().

The different values of the XML configuration can be accessed via Configuration#getBootstrapConfiguration(). This can for instance be helpful if you want to integrate Bean Validation into a managed environment and want to create managed instances of the objects configured via XML.

Using the fluent configuration API, you can override one or more of the settings when bootstrapping the factory. The following sections show how to make use of the different options. Note that the Configuration class exposes the default implementations of the different extension points which can be useful if you want to use these as delegates for your custom implementations.

8.2.1. `MessageInterpolator`

Message interpolators are used by the validation engine to create user readable error messages from constraint message descriptors.

In case the default message interpolation algorithm described in Chapter 4, Interpolating constraint error messages is not sufficient for your needs, you can pass in your own implementation of the MessageInterpolator interface via Configuration#messageInterpolator() as shown in Example 8.5, “Using a custom MessageInterpolator”.

Example 8.5. Using a custom MessageInterpolator

package org.hibernate.validator.referenceguide.chapter08;

public class MyMessageInterpolator implements MessageInterpolator {

	@Override
	public String interpolate(String messageTemplate, Context context) {
		//...
	}

	@Override
	public String interpolate(String messageTemplate, Context context, Locale locale) {
		//...
	}
}

ValidatorFactory validatorFactory = Validation.byDefaultProvider()
		.configure()
		.messageInterpolator( new MyMessageInterpolator() )
		.buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

8.2.2. `TraversableResolver`

In some cases the validation engine should not access the state of a bean property. The most obvious example for that is a lazily loaded property or association of a JPA entity. Validating this lazy property or association would mean that its state would have to be accessed, triggering a load from the database.

Which properties can be accessed and which ones not is controlled by querying the TraversableResolver interface. Example 8.6, “Using a custom TraversableResolver” shows how to use a custom traversable resolver implementation.

Example 8.6. Using a custom TraversableResolver

package org.hibernate.validator.referenceguide.chapter08;

public class MyTraversableResolver implements TraversableResolver {

	@Override
	public boolean isReachable(
			Object traversableObject,
			Node traversableProperty,
			Class<?> rootBeanType,
			Path pathToTraversableObject,
			ElementType elementType) {
		//...
	}

	@Override
	public boolean isCascadable(
			Object traversableObject,
			Node traversableProperty,
			Class<?> rootBeanType,
			Path pathToTraversableObject,
			ElementType elementType) {
		//...
	}
}

ValidatorFactory validatorFactory = Validation.byDefaultProvider()
		.configure()
		.traversableResolver( new MyTraversableResolver() )
		.buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

If no specific traversable resolver has been configured, the default behavior is to consider all properties as reachable and cascadable. When using Hibernate Validator together with a JPA 2 provider such as Hibernate ORM, only those properties will be considered reachable which already have been loaded by the persistence provider and all properties will be considered cascadable.

8.2.3. `ConstraintValidatorFactory`

ConstraintValidatorFactory is the extension point for customizing how constraint validators are instantiated and released.

The default ConstraintValidatorFactory provided by Hibernate Validator requires a public no-arg constructor to instantiate ConstraintValidator instances (see Section 6.1.2, “The constraint validator”). Using a custom ConstraintValidatorFactory offers for example the possibility to use dependency injection in constraint validator implementations.

To configure a custom constraint validator factory call Configuration#constraintValidatorFactory() (see Example 8.7, “Using a custom ConstraintValidatorFactory”.

Example 8.7. Using a custom ConstraintValidatorFactory

package org.hibernate.validator.referenceguide.chapter08;

public class MyConstraintValidatorFactory implements ConstraintValidatorFactory {

	@Override
	public <T extends ConstraintValidator<?, ?>> T getInstance(Class<T> key) {
		//...
	}

	@Override
	public void releaseInstance(ConstraintValidator<?, ?> instance) {
		//...
	}
}

ValidatorFactory validatorFactory = Validation.byDefaultProvider()
		.configure()
		.constraintValidatorFactory( new MyConstraintValidatorFactory() )
		.buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

Warning

Any constraint implementations relying on ConstraintValidatorFactory behaviors specific to an implementation (dependency injection, no no-arg constructor and so on) are not considered portable.

Note

ConstraintValidatorFactory implementations should not cache validator instances as the state of each instance can be altered in the initialize() method.

8.2.4. `ParameterNameProvider`

In case a method or constructor parameter constraint is violated, the ParameterNameProvider interface is used to retrieve the parameter name and make it available to the user via the property path of the constraint violation.

The default implementation returns parameter names in the form of arg0, arg1 etc, while custom implementations can retrieve the parameter names using methods such as parameter annotations, debug symbols, or Java 8 reflection.

An implementation for retrieving the parameter names using reflection in Java 8 is provided with ReflectionParameterNameProvider. For this parameter name provider to work, the source must be compiled using the –parameters compiler argument. Otherwise, the provider will return synthetic names in the form of arg0, arg1, etc.

To use ReflectionParameterNameProvider or another custom provider either pass an instance of the provider during bootstrapping as shown in Example 8.8, “Using a custom ParameterNameProvider”, or specify the fully qualified class name of the provider as value for the <parameter-name-provider> element in the META-INF/validation.xml file (see Section 7.1, “Configuring the validator factory in validation.xml”). This is demonstrated in Example 8.8, “Using a custom ParameterNameProvider”.

Example 8.8. Using a custom ParameterNameProvider

package org.hibernate.validator.referenceguide.chapter08;

public class MyParameterNameProvider implements ParameterNameProvider {

	@Override
	public List<String> getParameterNames(Constructor<?> constructor) {
		//...
	}

	@Override
	public List<String> getParameterNames(Method method) {
		//...
	}
}

ValidatorFactory validatorFactory = Validation.byDefaultProvider()
		.configure()
		.parameterNameProvider( new MyParameterNameProvider() )
		.buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

Tip

Hibernate Validator comes with a custom ParameterNameProvider implementation based on the ParaNamer library which provides several ways for obtaining parameter names at runtime. Refer to Section 11.10, “ParaNamer based ParameterNameProvider” to learn more about this specific implementation.

8.2.5. Adding mapping streams

As discussed earlier you can configure the constraints applying for your Java beans using XML based constraint mappings.

Besides the mapping files specified in META-INF/validation.xml you can add further mappings via Configuration#addMapping() (see Example 8.9, “Adding constraint mapping streams”). Note that the passed input stream(s) must adhere to the XML schema for constraint mappings presented in Section 7.2, “Mapping constraints via constraint-mappings”.

Example 8.9. Adding constraint mapping streams

InputStream constraintMapping1 = ...;
InputStream constraintMapping2 = ...;
ValidatorFactory validatorFactory = Validation.byDefaultProvider()
		.configure()
		.addMapping( constraintMapping1 )
		.addMapping( constraintMapping2 )
		.buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

You should close any passed input stream after the validator factory has been created.

8.2.6. Provider-specific settings

Via the configuration object returned by Validation#byProvider() provider specific options can be configured.

In case of Hibernate Validator this e.g. allows you to enable the fail fast mode and pass one or more programmatic constraint mappings as demonstrated in Example 8.10, “Setting Hibernate Validator specific options”.

Example 8.10. Setting Hibernate Validator specific options

ValidatorFactory validatorFactory = Validation.byProvider( HibernateValidator.class )
		.configure()
		.failFast( true )
		.addMapping( (ConstraintMapping) null )
		.buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

Alternatively, provider-specific options can be passed via Configuration#addProperty(). Hibernate Validator supports enabling the fail fast mode that way, too:

Example 8.11. Enabling a Hibernate Validator specific option via addProperty()

ValidatorFactory validatorFactory = Validation.byProvider( HibernateValidator.class )
		.configure()
		.addProperty( "hibernate.validator.fail_fast", "true" )
		.buildValidatorFactory();
Validator validator = validatorFactory.getValidator();

Refer to Section 11.2, “Fail fast mode” and Section 11.3, “Programmatic constraint declaration” to learn more about the fail fast mode and the constraint declaration API.

8.3. Configuring a Validator

When working with a configured validator factory it can occasionally be required to apply a different configuration to a single Validator instance. Example 8.12, “Configuring a Validator instance via usingContext()” shows how this can be achieved by calling ValidatorFactory#usingContext().

Example 8.12. Configuring a Validator instance via usingContext()

ValidatorFactory validatorFactory = Validation.buildDefaultValidatorFactory();

Validator validator = validatorFactory.usingContext()
		.messageInterpolator( new MyMessageInterpolator() )
		.traversableResolver( new MyTraversableResolver() )
		.getValidator();