Jakarta Validation - Lab 2

The goal is to illustrate how to create a custom validation in Java using Jakarta Validation. We're developing a custom validation called SalaryValidator and an associated annotation named SalaryConstraint.

This custom validation ensures that the Money field representing an employee's salary in the Worker class is non-null and greater than zero. This approach enhances data validation in Java applications, ensuring that salary values meet specific criteria and providing customized error messages for validation failures.

1. Create the custom constraint class

Steps

1. Open the 01-jakarta-ee project and navigate to the src/main/java
2. Create an interface called SalaryConstraint in the expert.os.labs.persistence.validation package

3. Add the following annotations to the interface where:

   • the @Constraint annotation come from the jakarta.validation package
   • the other annotations come from the java.lang.annotation package

   @Documented
   @Constraint(validatedBy = SalaryValidator.class)
   @Target( { ElementType.METHOD, ElementType.FIELD })
   @Retention(RetentionPolicy.RUNTIME)
   

   Warning

   The SalaryValidator.class doesn't exist yet. We will create it in the next steps. For now, let your IDE complain about this missing class.

4. Define the annotation attributes:

   • message, as the default message
   • groups as the class group

   • payload as the Payload from the jakarta.validation package

     String message() default "Invalid salary";
     Class<?>[] groups() default {};
     Class<? extends Payload>[] payload() default {};
     

Expected results

• A new class SalaryConstraint that will be used for the custom validation

Solution

Click to see...

import jakarta.validation.Constraint;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Documented
@Constraint(validatedBy = SalaryValidator.class)
@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface SalaryConstraint {

}

2. Create the custom validator class

Steps

1. Create a class SalaryValidator in the expert.os.labs.persistence.validation package

2. Make the class implements the ConstraintValidator interface, typing SalaryConstraint and the Money classes

   • the ConstraintValidator class comes from the jakarta.validation package
   • the Money class comes from the org.joda.money package

   public class SalaryValidator implements ConstraintValidator<SalaryConstraint, Money> {
   }
   

3. Implements the isValid method (because, probably, your IDE will complain about it!)

   Tip

   Name the Money parameter as salary for clarity purposes

   @Override
   public boolean isValid(Money salary, ConstraintValidatorContext constraintValidatorContext) {
      return false;
   }
   

4. Add the validation logic in the isValid method containing:

   • check if the salary is not null
   • check if the salary is not negative or zero

   Tips

   • both checks can be connected to an && operator
   • you can use the method isNegativeOrZero() from the value field

Expected results

• A new class SalaryValidator that will be used to validate if the salary is not null and greater than zero

Solution

Click to see...

import jakarta.validation.ConstraintValidator;
import jakarta.validation.ConstraintValidatorContext;
import org.joda.money.Money;

public class SalaryValidator implements ConstraintValidator<SalaryConstraint, Money> {
   @Override
   public boolean isValid(Money salary, ConstraintValidatorContext constraintValidatorContext) {
      return salary != null && salary.isNegativeOrZero();
   }
}

3. Add the salary field to the Worker class

Steps

1. Open the Worker class
2. Add a new field called salary of type Money from the org.joda.money package
3. Add the @SalaryValidator annotation to its field and associate the message attribute with the String Salary should be greater than zero
4. Add the field salary into the constructor
5. Add the getter and setter for the salary field
6. Add the field salary into the toString() method

Expected results

• The class Worker with a new field salary with a custom constraint

Solution

Click to see...

public class Worker {
   // previous fields ignored

   @SalaryConstraint(message = "Salary should be greater than zero")
   private Money salary;

   public Worker(String nickname, String name, boolean working, String bio, int age, String email, Money salary) {
      // previous attributes ignored
      this.salary = salary;
   }

   public void setSalary(Money salary) {
      this.salary = salary;
   }

   public void getSalary() {
      return salary;
   }
}

4. Add the salary field to the WorkerBuilder class

Steps

1. Open the WorkerBuilder class
2. Add a new field called salary of type Money from the org.joda.money package
3. Add a new method for the salary field
4. Include the salary field into the build() method

Expected results

• The class WorkerBuilder with a new field salary

Solution

Click to see...

public class WorkerBuilder {
   // previous fields ignored

   private Money salary;

   // previous methods ignored

   public WorkerBuilder salary(Money salary) {
      this.salary = salary;
      return this;
   }

   public Worker build() {
      return new Worker(nickname, name, working, bio, age, email, salary);
   }
}

5. Create a test for the salary constraint

Steps

1. Open the WorkerTest in the src/test/java at the expert.os.labs.persistence.validation package
2. Add a new test called shouldNotCreateWorkerWithNegativeSalary()
3. Implement the test setting a negative value to the salary() method from the builder
   • the negative value can be set using Money.of(CurrencyUnit.of("USD"), -10)
   • the assertion must validate if the message Salary should be greater than zero is present

Expected results

• A new test to validate the implementation of the custom validation for the salary field

Solution

Click to see...

@Test
void shouldNotCreateWorkerWithNegativeSalary() {
   Worker worker = Worker.builder()
   .nickname("jonhdoe")
   .name("John Doe")
   .working(true)
   .bio("I am a software engineer")
   .age(30)
   .email("john.doe@gmail.com")
   .salary(Money.of(CurrencyUnit.of("USD"), -10)).build();

   Set<ConstraintViolation<Worker>> violations = validator.validate(worker);

   Assertions.assertThat(violations).isNotEmpty().hasSize(1)
      .map(ConstraintViolation::getMessage).contains("Salary should be greater than zero");
}