Spring Boot Bootcamp – Workbooks and Challenges
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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.


Screen Shot 2022-05-21 at 11.34.42 PM.png

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


Screen Shot 2022-05-22 at 12.41.34 AM.png

Test Case 2


Screen Shot 2022-05-22 at 12.41.45 AM.png

Task 7

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

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