h:messages gives no output

Question

I'm learning about bean validation. I have created simple form with username and password input fields which are bound through backing bean to model (User) properties username and password. I have marked them with annotation:

@Id
@NotNull(message="Username cannot be empty")
private String username;
@NotNull(message="Password cannot be empty")
private String password;

Now on the page with that form I've put <h:messages/> inside <h:form>...</h:form>. I submit empty form, I am redirected to the same page (I have return null in action method in backing bean) but no messages are being displayed. What am I doing wrong?

Answer 1

Solution is instead of using @NotNull, use @Size because empty input field is actually empty string and not null.

Answer 2

If you'd like to get @NotNull to work, you indeed need to let JSF set empty strings as null. In JSF 2.0 you can do that by adding the following context param to the web.xml:

<context-param>
    <param-name>javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL</param-name>
    <param-value>true</param-value>
</context-param>

I can't tell from experience if that would trigger the @NotNull, but in theory it should. Give it a try.