vaadin-framework/uitest/src/main/java/com/vaadin/tests/components/datefield/DateFieldValidationError.java

package com.vaadin.tests.components.datefield;

import java.time.LocalDate;
import java.util.Locale;

import com.vaadin.annotations.Widgetset;
import com.vaadin.data.Binder;
import com.vaadin.server.VaadinRequest;
import com.vaadin.tests.components.AbstractTestUI;
import com.vaadin.ui.Button;
import com.vaadin.ui.DateField;
import com.vaadin.ui.Notification;

@Widgetset("com.vaadin.DefaultWidgetSet")
public class DateFieldValidationError extends AbstractTestUI {

    @Override
    protected void setup(VaadinRequest request) {
        DateField df = new DateField();
        df.setLocale(Locale.US);
        Binder<Void> binder = new Binder<>();
        binder.forField(df)
                .withValidator(
                        localDate -> localDate != null
                                && localDate.isAfter(LocalDate.now()),
                        "Invalid date")
                .bind(v -> LocalDate.now(), (v, t) -> {
                    /* NO-OP */
                });
        addComponent(df);
        addComponent(new Button("Validate", event -> Notification
                .show(binder.validate().isOk() ? "OK" : "Fail")));
    }

}