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    }