    001    // Copyright 2007 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.internal.services;
    016
    017    import org.apache.tapestry5.services.Request;
    018    import org.apache.tapestry5.services.Session;
    019
    020    /**
    021     * The "flash" strategy stores data inside the {@link Session session}, just like {@link
    022     * SessionPersistentFieldStrategy}, but also removes the values from the session on first use. In this way, a short-term
    023     * value (such as an error message) will "survive" from an action request to a render request and then disappear.
    024     */
    025    public class FlashPersistentFieldStrategy extends AbstractSessionPersistentFieldStrategy
    026    {
    027        /**
    028         * Prefix used to identify keys stored in the session.
    029         */
    030        static final String PREFIX = "flash:";
    031
    032        public FlashPersistentFieldStrategy(Request request)
    033        {
    034            super(PREFIX, request);
    035        }
    036
    037        @Override
    038        protected void didReadChange(Session session, String attributeName)
    039        {
    040            // For flash persistence, after reading a value, get rid of it.
    041            session.setAttribute(attributeName, null);
    042        }
    043
    044    }