    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
    015    package org.apache.tapestry5;
    016
    017    /**
    018     * Responsible for validation of a single field.
    019     *
    020     * @param <T>
    021     * @see Validator
    022     * @see org.apache.tapestry5.services.FieldValidatorDefaultSource
    023     */
    024    public 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    }