    001// Licensed under the Apache License, Version 2.0 (the "License");
    002// you may not use this file except in compliance with the License.
    003// You may obtain a copy of the License at
    004//
    005//     http://www.apache.org/licenses/LICENSE-2.0
    006//
    007// Unless required by applicable law or agreed to in writing, software
    008// distributed under the License is distributed on an "AS IS" BASIS,
    009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    010// See the License for the specific language governing permissions and
    011// limitations under the License.
    012
    013package org.apache.tapestry5.services;
    014
    015import java.util.Collection;
    016
    017/**
    018 * Defines how changes to fields (within components, within pages) may have their values persisted between requests.
    019 * Different implementations store the field values {@linkplain org.apache.tapestry5.internal.services.SessionPersistentFieldStrategy
    020 * in the session}, {@linkplain org.apache.tapestry5.internal.services.ClientPersistentFieldStrategy on the client}, or
    021 * elsewhere.
    022 */
    023public interface PersistentFieldStrategy
    024{
    025    /**
    026     * Posts a change of a persistent property.
    027     *
    028     * @param pageName    the name of the page containing the component
    029     * @param componentId the nested id path of the component (or null for the page's root component)
    030     * @param fieldName   the name of the field whose persistent value has changed
    031     * @param newValue    the new value for the field, possibly null
    032     */
    033    void postChange(String pageName, String componentId, String fieldName, Object newValue);
    034
    035    /**
    036     * Finds all persistent changes previously stored for the named page (for the current active session or client).
    037     */
    038    Collection<PersistentFieldChange> gatherFieldChanges(String pageName);
    039
    040    /**
    041     * Discards any saved changes for the name page. There is no expectation that data already gathered from the
    042     * strategy and presumably dumped into component instance fields will be affected, but future field access (within
    043     * this request or a later one) will show no data for the indicated page.
    044     *
    045     * @param pageName logical name of page whose field persistent data should be discarded
    046     */
    047    void discardChanges(String pageName);
    048}