JSR 303 – Bean Validation – Basic

JSR 303 – Bean Validation is defines a metadata model and API for JavaBean validation. The metadata is primarily in Annotation forms, with the possibility of being overridden or extended by XML descriptors. Hibernate Validator is the reference implementation of JSR 303.

The current version, as of August 2nd, 2012, of JSR303 is 1.0, and of  Hibernate Validator version is 4.0.1.

1. Example

A straightforward use of Bean Validation is to document and specify validation rules on JavaBean’s properties. In the below example, it is easy to deduce that field manufacturer, licensePlate and seatCount are mandatory while note is not. In addition, licencePlate must contain at least 2 and at most 14 characters; seatCount must be equal or higher than 2.

It is intuitive.

package com.mycompany;
 
import javax.validation.constraints.Min;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;
 
public class Car {
 
   @NotNull
   private String manufacturer;
 
   @NotNull
   @Size(min = 2, max = 14)
   private String licensePlate;
 
   @Min(2)
   private int seatCount;
 
   private int note;
 
   public Car(String manufacturer, String licencePlate, int seatCount, int note) {
        this.manufacturer = manufacturer;
        this.licensePlate = licencePlate;
        this.seatCount = seatCount;
        this.note = note;
   }
 
   //getters and setters ...
}

The next question is: when and how these above validation rules get executed and enforced. The key to answer lies in a name: Validator. Semantically, it is responsible for validating executing stated validation rules. Programmatically,  it is an instance of class javax.validation.Validator.  (Literally, Hibernate Validator includes a validator :D).

ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
validator = factory.getValidator();
 
Car car = new Car(null, "DD-AB-123", 4);
Set<ConstraintViolation<Car>> constraintViolations = validator.validate(car);

2. Bean Validation with Spring MVC

Bean Validation can be used together with Spring MVC to implement automatic input validation. By placing an @Valid annotation in front of a model attribute, Spring MVC will carry out validation automatically. Validation result is stored inside an BindingResult instance. For example:

@Autowired
Validator validator;
 
@RequestMapping ("some-url")
public String someMethod(@Valid @ModelAttribute ("AttributeName") SomeModel model, BindingResult result) {
    if (result.hasErrors()) {
       //do error handling
    }
}