Workbook 8.3

In this workbook, you will validate fields from incoming request bodies.

Launch the starter project

Task 1 (Review)

Inside POM.xml, add the spring-boot-starter-validation dependency. It provides the library of files needed to validate fields.

Task 2 (Review)

Apply validation constraints in the event of a blank name:

    @NotBlank(message = "Name cannot be blank")

or a blank phone number:

    @NotBlank(message = "Number cannot be blank")

Task 3

Recall that @Valid – based on your constraints – will validate field values that were obtained from the request body. Inside the RestController, apply the @Valid annotation where needed.

Task 4

In order to handle invalid field arguments, your global exception handler must inherit from ResponseEntityExceptionHandler

public class ApplicationExceptionHandler extends ResponseEntityExceptionHandler {

Now, override the inherited method handleMethodArgumentNotValid. Inside the method, access the result of the validation process as follows:

ex.getBindingResult().getAllErrors() //returns list of errors from validation process

Just like in section 3, the BindingResult carries the result of the validation, and getAllErrors returns a List of errors from the validation process.

For now, loop through each error inside the errors List and print its message.

    for (ObjectError error : ex.getBindingResult().getAllErrors()) {
        System.out.println(error.getDefaultMessage());
    } 

Choose an appropriate status code from Mozilla Status Codes and return it.

return new ResponseEntity<>(STATUS_CODE_HERE);

---

Test Case: POST: localhost:8080/contact

Request Body
{
    "name": "Tyrion Lannister",
    "phoneNumber": "        "
}

Postman

Terminal Output:

>> Phone number cannot be blank

Task 5

Inside ErrorResponse.java, convert your message field into a List.

    private LocalDateTime timestamp;
    private List<String> message; <--

Fix every error inside the ErrorResponse.java.

    public ErrorResponse(List<String> message) {
        this.message = message;
        this.timestamp = LocalDateTime.now();
    }

Fix the errors inside handleContactNotFoundException:

ErrorResponse error = new ErrorResponse(Arrays.asList(ex.getLocalizedMessage()));

Inside handleMethodArgumentNotValid:

• Append every error message from the BindingResult into a List<String>.
• Create an ErrorResponse object and return it.

---

Test Case: POST: localhost:8080/contact

Request Body
{
    "name": "       ",
    "phoneNumber": "        "
}

Response

Spring Boot serializes the message List into a JSON ARRAY type.

Good Luck!