Java Bean Validation

The Spring Framework provides support for the Java Bean Validation API.

Overview of Bean Validation

Bean Validation provides a common way of validation through constraint declaration and metadata for Java applications. To use it, you annotate domain model properties with declarative validation constraints which are then enforced by the runtime. There are built-in constraints, and you can also define your own custom constraints.

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

  • Java

  • Kotlin

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

Bean Validation lets you declare constraints as the following example shows:

  • Java

  • Kotlin

public class PersonForm {

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

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

A Bean Validation validator then validates instances of this class based on the declared constraints. See Bean Validation for general information about the API. See the Hibernate Validator documentation for specific constraints. 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 including the bootstrapping of a Bean Validation provider as a Spring bean. This lets you inject a jakarta.validation.ValidatorFactory or jakarta.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:

  • Java

  • XML

import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;

@Configuration
public class AppConfig {

	@Bean
	public LocalValidatorFactoryBean validator() {
		return new LocalValidatorFactoryBean();
	}
}
<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 Bean Validation provider, such as the Hibernate Validator, is expected to be present in the classpath and is automatically detected.

Injecting a Validator

LocalValidatorFactoryBean implements both jakarta.validation.ValidatorFactory and jakarta.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 jakarta.validation.Validator if you prefer to work with the Bean Validation API directly, as the following example shows:

  • Java

  • Kotlin

import jakarta.validation.Validator;

@Service
public class MyService {

	@Autowired
	private Validator validator;
}
import jakarta.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

  • Kotlin

import org.springframework.validation.Validator;

@Service
public class MyService {

	@Autowired
	private Validator validator;
}
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 jakarta.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

  • Kotlin

@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy=MyConstraintValidator.class)
public @interface MyConstraint {
}
@Target(AnnotationTarget.FUNCTION, AnnotationTarget.FIELD)
@Retention(AnnotationRetention.RUNTIME)
@Constraint(validatedBy = MyConstraintValidator::class)
annotation class MyConstraint

  • Java

  • Kotlin

import jakarta.validation.ConstraintValidator;

public class MyConstraintValidator implements ConstraintValidator {

	@Autowired;
	private Foo aDependency;

	// ...
}
import jakarta.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:

  • Java

  • XML

import org.springframework.validation.beanvalidation.MethodValidationPostProcessor;

@Configuration
public class AppConfig {

	@Bean
	public MethodValidationPostProcessor validationPostProcessor() {
		return new MethodValidationPostProcessor();
	}
}
<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, which can optionally also declare the validation groups to use. See MethodValidationPostProcessor for setup details with the Hibernate Validator and Bean Validation 1.1 providers.

Method validation relies on AOP Proxies around the target classes, either JDK dynamic proxies for methods on interfaces or CGLIB proxies. There are certain limitations with the use of proxies, some of which are described in Understanding AOP Proxies. In addition remember to always use methods and accessors on proxied classes; direct field access will not work.

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

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

  • Kotlin

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();
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 Spring MVC Validation Configuration.

Spring MVC 3 Validation

See Validation in the Spring MVC chapter.