Vaadin 8 converter

In Vaadin 7 I used the converters to format the data in my UI and BeanFieldGroup.
In Vaadin 8 "public interface Converter <PRESENTATION, MODEL>" says, "Converters must not have any side effects (never update UI from inside a Convert).".
How can I format the fields in my UI in Vaadin 8?

Check this blog post, specifically point 6. for how to use fluent API with Binder, e.g. withConverter.

https://vaadin.com/framework/whatsnew
 

 Thank you.
But, how could I convert a wrong value entered by a user to a correct value on screen?

Example:
In Vaadin 7, my users could enter, in a date field, 3112, 31/12, 31-12, 12/31/17, etc.. and with the converters i transformed it on 12/31/2017 on screeen.