    001    // Copyright 2006, 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.services;
    016
    017    import java.util.Collection;
    018
    019    /**
    020     * Defines how changes to fields (within components, within pages) may have their values persisted between requests.
    021     * Different implementations store the field values {@linkplain org.apache.tapestry5.internal.services.SessionPersistentFieldStrategy
    022     * in the session}, {@linkplain org.apache.tapestry5.internal.services.ClientPersistentFieldStrategy on the client}, or
    023     * elsewhere.
    024     */
    025    public interface PersistentFieldStrategy
    026    {
    027        /**
    028         * Posts a change of a persistent property.
    029         *
    030         * @param pageName    the name of the page containing the component
    031         * @param componentId the nested id path of the component (or null for the page's root component)
    032         * @param fieldName   the name of the field whose persistent value has changed
    033         * @param newValue    the new value for the field, possibly null
    034         */
    035        void postChange(String pageName, String componentId, String fieldName, Object newValue);
    036
    037        /**
    038         * Finds all persistent changes previously stored for the named page (for the current active session or client).
    039         */
    040        Collection<PersistentFieldChange> gatherFieldChanges(String pageName);
    041
    042        /**
    043         * Discards any saved changes for the name page. There is no expectation that data already gathered from the
    044         * strategy and persumably dumped into component instance fields will be affected, but future field access (within
    045         * this request or a later one) will show no data for the indicated page.
    046         *
    047         * @param pageName logical name of page whose field persistent data should be discarded
    048         */
    049        void discardChanges(String pageName);
    050    }