Vaadin 8: Locale-specific validation message example.

LocalizationExample.java

package com.vaadin.tests;

import com.vaadin.data.Binder;
import com.vaadin.data.ErrorMessageProvider;
import com.vaadin.data.HasValue;
import com.vaadin.data.ValueContext;
import com.vaadin.data.converter.StringToIntegerConverter;
import com.vaadin.server.VaadinRequest;
import com.vaadin.tests.data.bean.Person;
import com.vaadin.ui.Button;
import com.vaadin.ui.Label;
import com.vaadin.ui.TextField;
import com.vaadin.ui.UI;
import com.vaadin.ui.VerticalLayout;

import java.util.Locale;

/**
 * Created by elmot on 3/7/2017.
 */
public class LocalizationExample extends UI {
    @Override
    protected void init(VaadinRequest request) {
        TextField ageField = new TextField("Age");
        Binder<Person> binder = new Binder<>(Person.class);
        binder.forField(ageField)
                .withConverter(new StringToIntegerConverter("Not a number"))

                // also might be done with RangeValidator, with overridden getMessage()
                .withValidator(age -> (age >= 7) && (age <= 130),
                        new MyErrorMessageProvider(ageField))
                .bind(Person::getAge,Person::setAge);
        setContent(new VerticalLayout(ageField,new Button("Validate", event->binder.validate())));
        setLocale(Locale.GERMANY);
    }

    private static class MyErrorMessageProvider implements ErrorMessageProvider {
        private final HasValue<?> ageField;

        public MyErrorMessageProvider(HasValue<?> ageField) {
            this.ageField = ageField;
        }

        @Override
        public String apply(ValueContext context) {
            Locale locale = context.getLocale().orElse(Locale.US);
            if (Locale.GERMAN.getLanguage().equals(locale.getLanguage())) {
                return String.format(Locale.GERMAN, "Der Wert %s ist ung\u00fcltig. Bitte geben Sie eine Zahl zwischen 7 und 130 ein!", ageField.getValue());
            } else {
                return String.format(Locale.ENGLISH, "Value %s is invalid, please enter a number from 7 to 130!", ageField.getValue());
            }
        }
    }
}