Quick concepts of Java Bean Validation framework to get started

Java Bean validation is annotation based object validation framework.

To validate a bean we need to

• Place validation annotation on the fields to be validated. Other than fields we can also use them on method/constructor parameters, on method return type or on class level.
• Get an instance of javax.validation.Validator
• Call Validator#validate() method to trigger validation process

The validation annotations are also referred as 'constraints'.

Validator is the main interface to kick off the validation process and to find out validation errors (violations).

This specification has been defined as a part JSR 380, 349 and JSR 303.

The reference implementation is Hibernate Validator Engine. So we need following maven dependencies to run any validation related code:

pom.xml

<dependency>
   <groupId>org.hibernate.validator</groupId>
   <artifactId>hibernate-validator</artifactId>
   <version>6.2.0.Final</version>
</dependency>
<dependency>
   <groupId>org.glassfish</groupId>
   <artifactId>javax.el</artifactId>
   <version>3.0.0</version>
</dependency>

Working with constraints and validation violations

Creating bean with constraints:

import javax.validation.constraints.*;

 public class MyBean{
    @NotNull
    private String strField
    //getters and setters
 }

In the above, snippet we used @NotNull. This annotation is one of the the predefined constraint annotations.

Bootstrapping and getting instance of javax.validation.Validator

import javax.validation.*
    ....
    Configuration<?> config = Validation.byDefaultProvider().configure();
    ValidatorFactory factory = config.buildValidatorFactory();
    Validator validator = factory.getValidator();
    factory.close();

Perform validations

Validator validator = ...
    .....
    MyBean myBean MyBean();
    .....
    Set<ConstraintViolation<MyBean>> violations = validator.validate(myBean);
       violations.forEach(v -> System.out.println(v.getPropertyPath() +
                                                      "- " + v.getMessage()));

Complete Example

package com.logicbig.example;

import javax.validation.*;
import javax.validation.constraints.NotNull;

public class BeanFieldValidationExample {
    private static final Validator validator;

    static {
        Configuration<?> config = Validation.byDefaultProvider().configure();
        ValidatorFactory factory = config.buildValidatorFactory();
        validator = factory.getValidator();
        factory.close();
    }

    private static class MyBean {
        @NotNull
        private String str;

        public String getStr () {
            return str;
        }

        public void setStr (String str) {
            this.str = str;
        }
    }

    public static void main (String[] args) {
        MyBean myBean = new MyBean();
        validator.validate(myBean).stream()
                 .forEach(BeanFieldValidationExample::printError);
    }

    private static void printError (ConstraintViolation<MyBean> violation) {
        System.out.println(violation.getPropertyPath()
                            + " " + violation.getMessage());
    }
}

Output

str must not be null

As saw in above example, javax.validation.ConstraintViolation is used to access validation messages. This object also exposes other details about the validation errors.

Field-level vs Property-level constraints

In above example, we used constraint annotation @NotNull on field level. We can also put constraints on getters, unless if they are not defined with @Target having ElementType.METHOD.

Constraints used on getters are referred as 'property-level' constraints. In this case performing validation will be the same as described above i.e. by calling validator.validate(..) method and get the validation violations.

Property-level constrains example

package com.logicbig.example;

import javax.validation.*;
import javax.validation.constraints.NotNull;

public class BeanPropertyValidationExample {
    private static final Validator validator;

    static {
        Configuration<?> config = Validation.byDefaultProvider().configure();
        ValidatorFactory factory = config.buildValidatorFactory();
        validator = factory.getValidator();
        factory.close();
    }

    private static class MyBean {
        private String str;

        @NotNull
        public String getStr () {
            return str;
        }

        public void setStr (String str) {
            this.str = str;
        }
    }

    public static void main (String[] args) {
        MyBean myBean = new MyBean();
        validator.validate(myBean).stream()
                 .forEach(BeanPropertyValidationExample::printError);
    }

    private static void printError (ConstraintViolation<MyBean> violation) {
        System.out.println(violation.getPropertyPath()
                            + " " + violation.getMessage());
    }
}

Output

str must not be null

Example Project

Dependencies and Technologies Used:

• hibernate-validator 6.2.0.Final (Hibernate's Jakarta Bean Validation reference implementation)
   Version Compatibility: 5.0.0.Final - 6.2.0.FinalVersion List
  ×

  Version compatibilities of hibernate-validator with this example:

  groupId: org.hibernate
  artifactId: hibernate-validator
  (Reference implementation for Bean Validation 1.1)
  • 5.0.0.Final
  • 5.0.1.Final
  • 5.0.2.Final
  • 5.0.3.Final
  • 5.1.0.Final
  • 5.1.1.Final
  • 5.1.2.Final
  • 5.1.3.Final
  • 5.2.0.Final
  • 5.2.1.Final
  • 5.2.2.Final
  • 5.2.3.Final
  • 5.2.4.Final
  • 5.2.5.Final
  • 5.3.0.Final
  • 5.3.1.Final
  • 5.3.2.Final
  • 5.3.3.Final
  • 5.3.4.Final
  • 5.3.5.Final
  • 5.3.6.Final
  • 5.4.0.Final
  • 5.4.1.Final
  • 5.4.2.Final
  • 5.4.3.Final
  groupId: org.hibernate.validator
  artifactId: hibernate-validator
  (Reference implementation for Bean Validation 2.0)
  • 6.0.0.Final
  • 6.0.1.Final
  • 6.0.2.Final
  • 6.0.3.Final
  • 6.0.4.Final
  • 6.0.5.Final
  • 6.0.6.Final
  • 6.0.7.Final
  • 6.0.8.Final
  • 6.0.9.Final
  • 6.0.10.Final
  • 6.0.11.Final
  • 6.0.12.Final
  • 6.0.13.Final
  • 6.0.14.Final
  • 6.0.15.Final
  • 6.0.16.Final
  • 6.0.17.Final
  • 6.0.18.Final
  • 6.0.19.Final
  • 6.0.20.Final
  • 6.0.21.Final
  • 6.0.22.Final
  • 6.1.0.Final
  • 6.1.1.Final
  • 6.1.2.Final
  • 6.1.3.Final
  • 6.1.4.Final
  • 6.1.5.Final
  • 6.1.6.Final
  • 6.1.7.Final
  • 6.2.0.Final
  Version 7 and later:
  Jakarta Bean Validation 3.0
  jakarta.* packages

  Versions in green have been tested.

• javax.el 3.0.0 (Expression Language 3.0)
  
• JDK 8
• Maven 3.8.1