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    
015    package 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     */
026    public 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    }