Using converters

Converters are a completely new feature in Vaadin 7. They are used to convert between the UI and the data model type. For example, we can convert String to some other types such as Date, Integer, Boolean, or we can convert Date to Long type or we can create custom converter. They are also used as an initial validator. In this recipe, we will create a converter that converts Roman numerals to integer numbers. We will create both conversions, Roman to integer and vice versa. It will consist of text field for the Roman numeral, one button, and one label for converted value as shown in the following screenshot:

How to do it...

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

   public class Demo extends UI {…}

2. We start with the creation of the converter class. This class has to implement the Converter interface.

   public class RomanToIntegerConverter implements Converter<String, Integer> {…}

3. We need three maps. The first two maps are used for conversion from Roman numerals...