Validating & Converting User Input

binder.forField(emailField)
    // Explicit validator instance
    .withValidator(new EmailValidator(
        "This doesn't look like a valid email address"))
    .bind(Person::getEmail, Person::setEmail);

binder.forField(nameField)
    // Validator defined based on a lambda
    // and an error message
    .withValidator(
        name -> name.length() >= 3,
        "Name must contain at least three characters")
    .bind(Person::getName, Person::setName);

binder.forField(titleField)
    // Shorthand for requiring the field to be non-empty
    .asRequired("Every employee must have a title")
    .bind(Person::getTitle, Person::setTitle);

Label emailStatus = new Label();
emailStatus.getStyle().set("color", "Red");
binder.forField(emailField)
    .withValidator(new EmailValidator(
        "This doesn't look like a valid email address"))
    // Shorthand that updates the label based on the
    // status
    .withStatusLabel(emailStatus)
    .bind(Person::getEmail, Person::setEmail);

Label nameStatus = new Label();

binder.forField(nameField)
    // Define the validator
    .withValidator(
        name -> name.length() >= 3,
        "Name must contain at least three characters")
    // Define how the validation status is displayed
    .withValidationStatusHandler(status -> {
        nameStatus.setText(status
                .getMessage().orElse(""));
        nameStatus.setVisible(status.isError());
    })
    // Finalize the binding
    .bind(Person::getName, Person::setName);

binder.forField(emailField)
    .withValidator(new EmailValidator(
        "This doesn't look like a valid email address"))
    .withValidator(
        email -> email.endsWith("@acme.com"),
        "Only acme.com email addresses are allowed")
    .bind(Person::getEmail, Person::setEmail);

Binder<Trip> binder = new Binder<>(Trip.class);
DatePicker departing = new DatePicker();
departing.setLabel("Departing");
DatePicker returning = new DatePicker();
returning.setLabel("Returning");

// Store return date binding so we can
// revalidate it later
Binder.Binding<Trip, LocalDate> returningBinding =
    binder
       .forField(returning).withValidator(
               returnDate -> !returnDate
                       .isBefore(departing.getValue()),
               "Cannot return before departing")
       .bind(Trip::getReturnDate, Trip::setReturnDate);

// Revalidate return date when departure date changes
departing.addValueChangeListener(
        event -> returningBinding.validate());

// Disables all validators, both binder-level and binding-level
binder.setValidatorsDisabled(true);

// Disables validators for a single binding
binding.setValidatorsDisabled(true);

TextField yearOfBirthField =
    new TextField("Year of birth");

binder.forField(yearOfBirthField)
    .withConverter(
        new StringToIntegerConverter("Not a number"))
    .bind(Person::getYearOfBirth,
        Person::setYearOfBirth);

// Checkbox for marital status
Checkbox marriedField = new Checkbox("Married");

binder.forField(marriedField).withConverter(
  m -> m ? MaritalStatus.MARRIED : MaritalStatus.SINGLE,
  MaritalStatus.MARRIED::equals)
.bind(Person::getMaritalStatus,
    Person::setMaritalStatus);

binder.forField(yearOfBirthField)
    // Validator is run with the String value
    // of the field
    .withValidator(text -> text.length() == 4,
            "Doesn't look like a year")
    // Converter is only run for strings
    // with 4 characters
    .withConverter(new StringToIntegerConverter(
            "Must enter a number"))
    // Validator is run with the converted value
    .withValidator(year -> year >= 1900 && year < 2000,
            "Person must be born in the 20th century")
    .bind(Person::getYearOfBirth,
            Person::setYearOfBirth);

binder.forField(yearOfBirthField)
    .withConverter(
        Integer::valueOf,
        String::valueOf,
        // Text to use instead of the
        // NumberFormatException message
        "Enter a number")
    .bind(Person::getYearOfBirth,
            Person::setYearOfBirth);

class MyConverter
        implements Converter<String, Integer> {
    @Override
    public Result<Integer> convertToModel(
            String fieldValue, ValueContext context) {
        // Produces a converted value or an error
        try {
            // ok is a static helper method that
            // creates a Result
            return Result.ok(Integer.valueOf(
                    fieldValue));
        } catch (NumberFormatException e) {
            // error is a static helper method
            // that creates a Result
            return Result.error("Enter a number");
        }
    }

    @Override
    public String convertToPresentation(
            Integer integer, ValueContext context) {
        // Converting to the field type should
        // always succeed, so there is no support for
        // returning an error Result.
        return String.valueOf(integer);
    }
}

// Using the converter
binder.forField(yearOfBirthField)
  .withConverter(new MyConverter())
  .bind(Person::getYearOfBirth, Person::setYearOfBirth);

@Tag("date-picker-demo")
public class DatePickerDemo implements HasValidator<LocalDate> /*, HasValue<...>*/ {

    // Each web component has a way to communicate its validation status
    // to its server-side component instance. The following `clientSideValid`
    // state is introduced here only for the sake of simplicity of this code
    // snippet:
    private boolean clientSideValid = true;

     /**
      * Note how <code>clientSideValid</code> engaged in the definition
      * of this method. It's important to reflect this status either
      * in the returning validation result of this method or any other
      * validation that's associated with this component.
      */
     @Override
     public Validator getDefaultValidator() { // (1)
          return (value, valueContext) -> clientSideValid ? ValidationResult.ok()
                  : ValidationResult.error("Invalid date format");
     }

     private final Collection<ValidationStatusChangeListener<LocalDate>>
         validationStatusListeners = new ArrayList<>();

     /**
      * This enables the binding to subscribe for the validation status
      * change events that are fired by this component and revalidate
      * itself respectively.
      */
     @Override
     public Registration addValidationStatusChangeListener(
             ValidationStatusChangeListener<LocalDate> listener) {
         validationStatusListeners.add(listener);
         return () -> validationStatusListeners.remove(listener);
     }

     protected void fireValidationStatusChangeEvent(
             boolean newValidationStatus) {
         if (this.clientSideValid != newValidationStatus) {
             this.clientSideValid = newValidationStatus;
             var event = new ValidationStatusChangeEvent<>(this,
                     newValidationStatus);
             validationStatusListeners.forEach(
                     listener -> listener.validationStatusChanged(event));
         }
     }
 }