001// Copyright 2006, 2008, 2011 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
017import org.apache.tapestry5.services.FormSupport;
018
019/**
020 * Translates between client-side and server-side values. Client-side values are always strings.
021 * 
022 * @param <T> the type being translated
023 * @see org.apache.tapestry5.services.TranslatorSource
024 * @see org.apache.tapestry5.FieldValidationSupport
025 * @see org.apache.tapestry5.FieldTranslator
026 */
027public interface Translator<T>
028{
029    /**
030     * Returns a unique name for the translator. This is used to identify the translator by name, but is also used when
031     * locating override messages for the translator.
032     * 
033     * @return unique name for the translator
034     */
035    String getName();
036
037    /**
038     * Converts a server-side value to a client-side string. This allows for formatting of the value in a way
039     * appropriate to the end user. The output client value should be parsable by
040     * {@link #parseClient(Field, String, String)}.
041     * 
042     * @param value
043     *            the server side value (which will not be null)
044     * @return client-side value to present to the user
045     */
046    String toClient(T value);
047
048    /**
049     * Returns the type of the server-side value.
050     * 
051     * @return a type
052     */
053    Class<T> getType();
054
055    /**
056     * Returns the message key, within the application's global message catalog, normally used by this validator. This
057     * is used to provide the formatted message to {@link #parseClient(Field, String, String)} or
058     * {@link #render(Field, String, MarkupWriter, org.apache.tapestry5.services.FormSupport)}.
059     * 
060     * @return a message key
061     */
062    String getMessageKey();
063
064    /**
065     * Converts a submitted request value into an appropriate server side value.
066     * 
067     * @param field
068     *            for which a value is being parsed
069     * @param clientValue
070     *            to convert to a server value; this will not be null, but may be blank
071     * @param message
072     *            formatted validation message, either from validation messages, or from an override
073     * @return equivalent server-side value (possibly null)
074     * @throws ValidationException
075     *             if the value can not be parsed
076     */
077    T parseClient(Field field, String clientValue, String message) throws ValidationException;
078
079    /**
080     * Hook used by components to allow the validator to contribute additional attributes or (more often) client-side
081     * JavaScript (via the
082     * {@link org.apache.tapestry5.services.FormSupport#addValidation(Field, String, String, Object)}).
083     * 
084     * @param field
085     *            the field which is currently being rendered
086     * @param message
087     *            formatted validation message, either from validation messages, or from an override
088     * @param writer
089     *            markup writer, allowing additional attributes to be written into the active element
090     * @param formSupport
091     *            used to add JavaScript
092     */
093    void render(Field field, String message, MarkupWriter writer, FormSupport formSupport);
094}