    001// Licensed to the Apache Software Foundation (ASF) under one
    002// or more contributor license agreements.  See the NOTICE file
    003// distributed with this work for additional information
    004// regarding copyright ownership.  The ASF licenses this file
    005// to you under the Apache License, Version 2.0 (the
    006// "License"); you may not use this file except in compliance
    007// with the License.  You may obtain a copy of the License at
    008//
    009// http://www.apache.org/licenses/LICENSE-2.0
    010//
    011// Unless required by applicable law or agreed to in writing,
    012// software distributed under the License is distributed on an
    013// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    014// KIND, either express or implied.  See the License for the
    015// specific language governing permissions and limitations
    016// under the License.
    017
    018package org.apache.tapestry5.services;
    019
    020/**
    021 * Used by {@link ApplicationStateManager} to manage a specific kind of Session State Object (SSO)
    022 * persistence. The
    023 * strategy is responsible for managing SSO instances within its domain.
    024 * <p>
    025 * <em>NOTE: The term "Application" here is a hold-over from Tapestry 5.0, which used the @ApplicationState
    026 * (deprecated and deleted) annotation, and called them "ASOs" (Application State Objects). This service
    027 * would be better named "SessionStatePersistenceStrategy" (but renaming it would cause backwards
    028 * compatibility issues).</em>
    029 *
    030 * @see org.apache.tapestry5.services.ApplicationStatePersistenceStrategySource
    031 */
    032public interface ApplicationStatePersistenceStrategy
    033{
    034    /**
    035     * Gets the SSO from the domain. If the SSO does not already exist, it is created and stored, then returned.
    036     */
    037    <T> T get(Class<T> ssoClass, ApplicationStateCreator<T> creator);
    038
    039    /**
    040     * Stores a new SSO, possibly replacing the existing one.
    041     *
    042     * @param <T>
    043     * @param ssoClass
    044     * @param sso      instance to store, or null to delete existing
    045     */
    046    <T> void set(Class<T> ssoClass, T sso);
    047
    048    /**
    049     * Returns true if the SSO already exists, false if null.
    050     */
    051    <T> boolean exists(Class<T> ssoClass);
    052
    053    /**
    054     * Returns the SSO if it exists or null.
    055     */
    056    default <T> T getIfExists(Class<T> ssoClass) {
    057        return exists(ssoClass) ? get(ssoClass, () -> null) : null;
    058    }
    059}