Using field validation

People make mistakes. Therefore, we have to check the user input. The important reason for validation is to make sure the data that should be stored in the database conforms to the rules of the data model. In Vaadin, it is possible to do it in several ways. The easiest way is to use predefined validators. We can validate, for example, the length of the string or the size of values; or we can compare the string against a regular expression. In this recipe, we will create a field that will check whether the given string is a syntactically valid email address.

How to do it...

Carry out the following steps to learn how to use validation in the form fields:

1. Create a Vaadin project with the main UI class called Demo.

   public class Demo extends UI {…}

2. We start with the main class named EmailField. This class is based on the TextField class. In the constructor, we set the caption of the field. We set this component to an immediate mode for a quick response. Through the addValidator...