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}