001// Copyright 2005 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.tapestry;
016
017/**
018 * <em>Optional</em> interface implemented by Application State Objects. This interface allows
019 * Tapestry to optimize the storage of the objects into the
020 * {@link org.apache.tapestry.web.WebSession session}, only storing the objects when they require
021 * storage due to a change in internal state.
022 * 
023 * @author Howard M. Lewis Ship
024 * @since 4.0
025 */
026public interface SessionStoreOptimized
027{
028    /**
029     * Queried by the {@link org.apache.tapestry.engine.state.StateObjectManager} to see if the
030     * object actually needs to be stored. Objects that implement this interface should store an
031     * internal flag. The flag should be set when any change to the object's internal state occurs.
032     * The flag should be cleared when the object is stored into the session (typically, by
033     * implementing {@link javax.servlet.http.HttpSessionBindingListener}.
034     * 
035     * @return true if the object needs to be stored back into the session, false if the internal
036     *         state of the object is unchanged
037     */
038    boolean isStoreToSessionNeeded();
039
040}