    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
    015    package 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     */
    024    public 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    }