001    // Copyright 2007, 2008 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.services;
016    
017    /**
018     * Used by {@link ApplicationStateManager} to manage a specific kind of Session State Object (SSO) persistence. The
019     * stategy is responsible for managing SSO instances within its domain.
020     *
021     * @see org.apache.tapestry5.services.ApplicationStatePersistenceStrategySource
022     */
023    public interface ApplicationStatePersistenceStrategy
024    {
025        /**
026         * Gets the SSO from the domain. If the ASO does not already exist, it is created and stored, then returned.
027         */
028        <T> T get(Class<T> ssoClass, ApplicationStateCreator<T> creator);
029    
030        /**
031         * Stores a new SSO, possibly replacing the existing one.
032         *
033         * @param <T>
034         * @param ssoClass
035         * @param sso      instance to store, or null to delete existing
036         */
037        <T> void set(Class<T> ssoClass, T sso);
038    
039        /**
040         * Returns true if the SSO already exists, false if null.
041         */
042        <T> boolean exists(Class<T> ssoClass);
043    }