First validation example

In the following example, we are going to show how to use the bean validation API to validate our application beans against a set of constraints. Recalling our Movie entity, we are going to force the user to give each movie title a value, banning him/her from letting it be a null value. This makes sense, as of course there will never be a movie with no title at all. Let's see how we can do this with the bean validation API.

Well, in fact, it's too simple. We will just annotate the title field with the @NotNull annotation, part of a set of built-in constraints provided with the bean validation API, as shown in the following example:

@Entity 
public class Movie { 
    .... 
    @NotNull 
    private String title; 
    .... 
} 

@NotNull is used to check whether the variable has a value or not; if the variable has a value, then the bean is considered to be in a valid state. Otherwise, if it's null, the bean is considered to be in an invalid state.

But how and when will bean...