13.6. Studio: Spa User Validation

We’ll build on the User Signup studio from last class, adding in model validation.

13.6.1. Getting Started

Open up your spa-day application and checkout the user-signup-pt2 branch.

13.6.2. Add Validation Annotations

Navigate to the User model class. Add validation annotations to ensure these conditions are satisfied:

  1. Username, password, and verify are required (they can’t be empty)
  2. Username is between 5 and 15 characters
  3. Email is optional
  4. If provided, the email has the format of a valid email address.
  5. The password is at least 6 characters long

13.6.3. Using the Model to Render the Form

In the UserController, modify the add method that displays the form so that it passes in an empty User object with:

model.addAttribute(new User());

This object will be accessible in the template, by name, as user.


Now that you’re passing in an empty User object, you may notice some redundant code in your processAddUserForm controller. Remove the model attribute additions and update the user/add template to make use of the model fields (eg. user.username).

While you’re in the add.html template remove the type="email" designation from the email input. The last studio had you add this type to provide some client-side validation on the email field, but we shouldn’t consider that sufficient. Now that we know how to use model validation to validate an email field, we’ll favor this technique over client-side validation. Even with client-side validation (that is, in the browser), you should always validate data on the server as well. You might want to provide constraints in addition to or beyond what the browser does, and it’s also possible for a clever (or, more often, malicious) user to bypass the browser’s validation. For this studio, we’ll remove the input type to make it easier to test the server-side validation.

13.6.4. Validating Form Submission Data

Now that you have your form set up, go back to UserController and add validation on form submission by adding the @Valid annotation to the User parameter that is bound, along with an additional parameter: Errors errors.


Remember, you must put this parameter directly after the User parameter in the method definition for it to work properly.

Within the processAddUserForm handler, check for errors configured by the validation annotation using errors.hasErrors(). If this returns true, return the user to the form. Validating That Passwords Match

As we mentioned above, we are not able to use Spring’s validation machinery to validate that the two password fields match given the setup we have here. Checking errors.hasErrors() will only tell us if there are errors in other form data fields.

Last studio, we added some validation checks to make sure the password fields match. Now we have two validation sections: one for the annotation-configured validation (which checks errors.hasErrors()), and one that checks that the password fields match. Make sure they work in-sync with each other to properly return to the form if any of the validation conditions fail.


You can, in fact, validate that passwords match using annotations by taking a slightly more difficult approach than we’ve done here. We outline how to do so in the Bonus Mission section.

13.6.5. Test, Test, Test!

You made a lot of changes! Be sure to thoroughly test them to make sure everything works as expected.

13.6.6. Bonus Mission

Let’s set up our User class so we can validate that the password fields match using annotations.

  1. Add a private String verifyPassword field to User, along with getters and setters.
  2. Add a new method, private void checkPassword, that compares password and verifyPassword. If neither is null and they don’t match, then set verifyPassword = null.
  3. In both setPassword and setVerifyPassword, call checkPassword after setting the given field.
  4. Add @NotNull to the verifyPassword field with the error message: “Passwords do not match”.
  5. Refactor the controller and add.html template to use the built-in, annotation-based validation instead of the manual password validation that we carried out previously. Be sure to update the verify field and label in the form to use the field on the User class, and to remove String verify from the add method signature.

The result of these changes is that when the User object is bound to the request, both password and verifyPassword are set. Spring does this by calling the setters on these fields. The setters call checkPassword, so when the second one is set (whichever that may be), we’ll know that both password and verifyPassword are not null and we’ll compare them. If they don’t match, we manually violate the @NotNull validation on verifyPassword by setting that field to null.