Spring Validation

Spring 3 introduced several enhancements to its validation support. First, the JSR-303 Bean Validation API is fully supported. Second, when used programmatically, Spring’s DataBinder can validate objects as well as bind to them. Third, Spring MVC has support for declaratively validating @Controller inputs.

Overview of the JSR-303 Bean Validation API

JSR-303 standardizes validation constraint declaration and metadata for the Java platform. By using this API, you annotate domain model properties with declarative validation constraints and the runtime enforces them. You can use a number of built-in constraints. You can also define your own custom constraints.

Consider the following example, which shows a simple PersonForm model with two properties:

Java
public class PersonForm {
	private String name;
	private int age;
}
Kotlin
class PersonForm(
		private val name: String,
		private val age: Int
)

JSR-303 lets you define declarative validation constraints against such properties, as the following example shows:

Java
public class PersonForm {

	@NotNull
	@Size(max=64)
	private String name;

	@Min(0)
	private int age;
}
Kotlin
class PersonForm(
	@get:NotNull @get:Size(max=64)
	private val name: String,
	@get:Min(0)
	private val age: Int
)

When a JSR-303 Validator validates an instance of this class, these constraints are enforced.

For general information on JSR-303 and JSR-349, see the Bean Validation website. For information on the specific capabilities of the default reference implementation, see the Hibernate Validator documentation. To learn how to set up a bean validation provider as a Spring bean, keep reading.

Configuring a Bean Validation Provider

Spring provides full support for the Bean Validation API. This includes convenient support for bootstrapping a JSR-303 or JSR-349 Bean Validation provider as a Spring bean. This lets you inject a javax.validation.ValidatorFactory or javax.validation.Validator wherever validation is needed in your application.

You can use the LocalValidatorFactoryBean to configure a default Validator as a Spring bean, as the following example shows:

<bean id="validator"
	class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean"/>

The basic configuration in the preceding example triggers bean validation to initialize by using its default bootstrap mechanism. A JSR-303 or JSR-349 provider, such as the Hibernate Validator, is expected to be present in the classpath and is automatically detected.

Injecting a Validator

LocalValidatorFactoryBean implements both javax.validation.ValidatorFactory and javax.validation.Validator, as well as Spring’s org.springframework.validation.Validator. You can inject a reference to either of these interfaces into beans that need to invoke validation logic.

You can inject a reference to javax.validation.Validator if you prefer to work with the Bean Validation API directly, as the following example shows:

Java
import javax.validation.Validator;

@Service
public class MyService {

	@Autowired
	private Validator validator;
}
Kotlin
import javax.validation.Validator;

@Service
class MyService(@Autowired private val validator: Validator)

You can inject a reference to org.springframework.validation.Validator if your bean requires the Spring Validation API, as the following example shows:

Java
import org.springframework.validation.Validator;

@Service
public class MyService {

	@Autowired
	private Validator validator;
}
Kotlin
import org.springframework.validation.Validator

@Service
class MyService(@Autowired private val validator: Validator)

Configuring Custom Constraints

Each bean validation constraint consists of two parts: * A @Constraint annotation that declares the constraint and its configurable properties. * An implementation of the javax.validation.ConstraintValidator interface that implements the constraint’s behavior.

To associate a declaration with an implementation, each @Constraint annotation references a corresponding ConstraintValidator implementation class. At runtime, a ConstraintValidatorFactory instantiates the referenced implementation when the constraint annotation is encountered in your domain model.

By default, the LocalValidatorFactoryBean configures a SpringConstraintValidatorFactory that uses Spring to create ConstraintValidator instances. This lets your custom ConstraintValidators benefit from dependency injection like any other Spring bean.

The following example shows a custom @Constraint declaration followed by an associated ConstraintValidator implementation that uses Spring for dependency injection:

Java
@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy=MyConstraintValidator.class)
public @interface MyConstraint {
}
Kotlin
@Target(AnnotationTarget.FUNCTION, AnnotationTarget.FIELD)
@Retention(AnnotationRetention.RUNTIME)
@Constraint(validatedBy = MyConstraintValidator::class)
annotation class MyConstraint
Java
import javax.validation.ConstraintValidator;

public class MyConstraintValidator implements ConstraintValidator {

	@Autowired;
	private Foo aDependency;

	// ...
}
Kotlin
import javax.validation.ConstraintValidator

class MyConstraintValidator(private val aDependency: Foo) : ConstraintValidator {

	// ...
}

As the preceding example shows, a ConstraintValidator implementation can have its dependencies @Autowired as any other Spring bean.

Spring-driven Method Validation

You can integrate the method validation feature supported by Bean Validation 1.1 (and, as a custom extension, also by Hibernate Validator 4.3) into a Spring context through a MethodValidationPostProcessor bean definition, as follows:

<bean class="org.springframework.validation.beanvalidation.MethodValidationPostProcessor"/>

To be eligible for Spring-driven method validation, all target classes need to be annotated with Spring’s @Validated annotation. (Optionally, you can also declare the validation groups to use.) See the MethodValidationPostProcessor javadoc for setup details with the Hibernate Validator and Bean Validation 1.1 providers.

Additional Configuration Options

The default LocalValidatorFactoryBean configuration suffices for most cases. There are a number of configuration options for various Bean Validation constructs, from message interpolation to traversal resolution. See the LocalValidatorFactoryBean javadoc for more information on these options.

Configuring a DataBinder

Since Spring 3, you can configure a DataBinder instance with a Validator. Once configured, you can invoke the Validator by calling binder.validate(). Any validation Errors are automatically added to the binder’s BindingResult.

The following example shows how to use a DataBinder programmatically to invoke validation logic after binding to a target object:

Java
Foo target = new Foo();
DataBinder binder = new DataBinder(target);
binder.setValidator(new FooValidator());

// bind to the target object
binder.bind(propertyValues);

// validate the target object
binder.validate();

// get BindingResult that includes any validation errors
BindingResult results = binder.getBindingResult();
Kotlin
val target = Foo()
val binder = DataBinder(target)
binder.validator = FooValidator()

// bind to the target object
binder.bind(propertyValues)

// validate the target object
binder.validate()

// get BindingResult that includes any validation errors
val results = binder.bindingResult

You can also configure a DataBinder with multiple Validator instances through dataBinder.addValidators and dataBinder.replaceValidators. This is useful when combining globally configured bean validation with a Spring Validator configured locally on a DataBinder instance. See [validation-mvc-configuring].

Spring MVC 3 Validation

See Validation in the Spring MVC chapter.