    001// Copyright 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 * Defines a strategy, used by {@link Field} components such as {@link org.apache.tapestry5.corelib.components.TextField},
    019 * to handle the case where either the server-side value to be sent (as a string) to the client, or the client-side
    020 * string passed back up to the server, is null or blank.
    021 *
    022 * @see org.apache.tapestry5.services.NullFieldStrategySource
    023 */
    024public interface NullFieldStrategy
    025{
    026    /**
    027     * Provides a replacement value for null, when converting the server-side object to a client-side string. The
    028     * replacement value, if non-null, will be passed to {@link org.apache.tapestry5.Translator#toClient(Object)}.
    029     */
    030    Object replaceToClient();
    031
    032    /**
    033     * Provides a replacement value for a null or blank string passed from the client to the server as part of a form
    034     * submission. This replacement value will be passed to {@link Translator#parseClient(Field, String, String)}  as if
    035     * it were the value supplied by the user.
    036     *
    037     * @return replacement value (this must not be null)
    038     */
    039    String replaceFromClient();
    040}