Now, let's move on to create the RegistrationPayload class itself. Here is how it looks:

...
public class RegistrationPayload {

  @Size(min = 2, max = 50, message = "Username must be between 2 and 50 characters")
  @NotNull
  private String username;

  @Email(message = "Email address should be valid")
  @Size(max = 100, message = "Email address must not be more than 100 characters")
  @NotNull
  private String emailAddress;

  @Size(min = 6, max = 30, message = "Password must be between 6 and 30 characters")
  @NotNull
  private String password;

  // getters and setters
}

As you can see, this RegistrationPayload class has three fields and the constraints we apply to them match those we added on the frontend. One difference is that the @Size annotation considers a null value to be valid. That's why we have to put the @NotNull annotation for each field too.

We will also need to add the following test methods in RegistrationPayloadTests to cover every constraint applied on each field:

• validate_payloadWithInvalidEmail_shouldFail()
• validate_payloadWithEmailAddressLongerThan100_shouldFail()
• validate_payloadWithUsernameShorterThan2_shouldFail()
• validate_payloadWithUsernameLongerThan50_shouldFail()
• validate_payloadWithPasswordShorterThan6_shouldFail()
• validate_payloadWithPasswordLongerThan30_shouldFail()

We will not go through each test method here. If you're interested in the implementation of these methods, you can find them in the commit history on GitHub.