    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
    015package org.apache.tapestry5.internal.services;
    016
    017import org.apache.tapestry5.http.services.Request;
    018import org.apache.tapestry5.http.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 */
    025public 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}