Workbook 3.3

In this workbook, you will create a custom constraint annotation.

Task 1

Add the custom Age annotation:

• It is applied at the FIELD level.
• It is retained at RUNTIME.
• It carries a default message of "INVALID AGE";

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Age {

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

}

Task 2

Apply the annotation on the dateOfBirth field, and override the default message.

    @Age(message = "Must be at least 18")

Task 3

As it stands, the annotation isn't connected to any constraint validation logic. Create an AgeValidator class, and specify that Age is a @Constraint that's connected to it.

@Constraint(validatedBy =  AgeValidator.class)

Inside AgeValidator.java, implement the validation logic using the code below. See the cheat sheet if you forgot how to set up a validator.

     long diff = new Date().getTime() - value.getTime();
     int age = (int) (TimeUnit.MILLISECONDS.toDays(diff) / 365);

Make the necessary changes inside the HTML to achieve the following output.

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Task 4

The username cannot contain any special characters $ % # @ ^ * or uppercase letters. Define another annotation named Username. Once again, the annotation will be:

• applied at the FIELD level.
• retained at RUNTIME.
• carry a default message of "INVALID USERNAME";

Task 5

Apply the annotation on the username field, and override the default messsage.

    @Username(message = "Cannot contain special characters or uppercase characters ")

Task 6

Define the annotation as a @Constraint that's connected to the UsernameValidator class. Use the following code to Implement the validation logic:

    import java.util.regex.Matcher;
    import java.util.regex.Pattern;
                                         
    Pattern pattern = Pattern.compile("[^a-z0-9 ]");
    Matcher matcher = pattern.matcher(value);
    boolean badCharacters = matcher.find(); //false if characters are a-z or 0-9

Make the necessary changes to achieve the following output.

Test Case 1

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Test Case 2

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Task 7

Place the annotation and validator classes in a single folder called validation.