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    }