    001// Copyright 2006, 2007, 2008 The Apache Software Foundation
    002//
    003// Licensed under the Apache License, Version 2.0 (the "License");
    004// you may not use this file except in compliance with the License.
    005// You may obtain a copy of the License at
    006//
    007//     http://www.apache.org/licenses/LICENSE-2.0
    008//
    009// Unless required by applicable law or agreed to in writing, software
    010// distributed under the License is distributed on an "AS IS" BASIS,
    011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012// See the License for the specific language governing permissions and
    013// limitations under the License.
    014
    015package org.apache.tapestry5;
    016
    017/**
    018 * Responsible for validation of a single field.
    019 *
    020 * @param <T> the type of the values being validated
    021 * @see Validator
    022 * @see org.apache.tapestry5.services.FieldValidatorDefaultSource
    023 */
    024public interface FieldValidator<T>
    025{
    026    /**
    027     * Invoked after the client-submitted value has been {@link Translator translated} to check that the value conforms
    028     * to expectations (often, in terms of minimum or maximum value). If and only if the value is approved by all
    029     * Validators is the value applied by the field.
    030     *
    031     * @param value the translated value supplied by the user
    032     * @throws ValidationException if the value violates the constraint
    033     */
    034    void validate(T value) throws ValidationException;
    035
    036    /**
    037     * Invokes {@link Validator#render(Field, Object, org.apache.tapestry5.ioc.MessageFormatter, MarkupWriter,
    038     * org.apache.tapestry5.services.FormSupport)}. This is called at a point "inside" the tag, so that additional
    039     * attributes may be added.  In many cases, the underlying {@link org.apache.tapestry5.Validator} may write
    040     * client-side JavaScript to enforce the constraint as well.
    041     *
    042     * @param writer markup writer to direct output to.
    043     * @see org.apache.tapestry5.MarkupWriter#attributes(Object[])
    044     */
    045    void render(MarkupWriter writer);
    046
    047    /**
    048     * Returns true if any underlying {@link org.apache.tapestry5.Validator} returns true from {@link
    049     * org.apache.tapestry5.Validator#isRequired()}.
    050     *
    051     * @return true if the field is required   (a non-blank value is expected)
    052     */
    053    boolean isRequired();
    054}