001// Copyright 2007, 2008, 2010 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.services;
016
017import org.apache.tapestry5.ioc.ObjectLocator;
018import org.apache.tapestry5.ioc.annotations.UsesMappedConfiguration;
019
020/**
021 * Responsible for managing <em>session state objects</em>, objects which persist between requests, but are not tied to
022 * any individual page or component. SSOs are also created on demand. SSOs are typically stored in the session, so that
023 * they are specific to a particular client.
024 * <p/>
025 * The term "Application" is a hold-over from Tapestry 5.0, which used the @ApplicationState (deprecated and deleted)
026 * annotation, and called them "ASOs" (Application State Objects). This service would be better named
027 * "SessionStateManager" (but renaming it would cause backwards compatibility issues).
028 * <p/>
029 * Tapestry has a built-in default strategy for storing SSOs (in the session) and instantiating them. If desired,
030 * contributions to the service configuration can override the default behavior, either specifying an alternate storage
031 * strategy, or an alternate {@linkplain org.apache.tapestry5.services.ApplicationStateCreator creation strategy}.
032 * 
033 * @see org.apache.tapestry5.annotations.SessionState
034 */
035@UsesMappedConfiguration(key = Class.class, value = ApplicationStateContribution.class)
036public interface ApplicationStateManager
037{
038    /**
039     * For a given class, find the SSO for the class, creating it if necessary. The manager has a configuration that
040     * determines how an instance is stored and created as needed. The default (when there is no configuration for
041     * a SSO type) is to instantiate the object with injected dependencies, via {@link ObjectLocator#autobuild(Class)}.
042     * This
043     * allows an SSO to keep references to Tapestry IoC services or other objects that can be injected.
044     * 
045     * @param ssoClass
046     *            identifies the SSO to access or create
047     * @return the SSO instance
048     */
049    <T> T get(Class<T> ssoClass);
050
051    /**
052     * For a given class, find the SSO for the class. The manager has a configuration that determines how an instance is
053     * stored.
054     * 
055     * @param ssoClass
056     *            identifies the SSO to access or create
057     * @return the SSO instance or null if it does not already exist
058     */
059    <T> T getIfExists(Class<T> ssoClass);
060
061    /**
062     * Returns true if the SSO already exists, false if it has not yet been created.
063     * 
064     * @param ssoClass
065     *            used to select the SSO
066     * @return true if SSO exists, false if null
067     */
068    <T> boolean exists(Class<T> ssoClass);
069
070    /**
071     * Stores a new SSO, replacing the existing SSO (if any). Storing the value null will delete the SSO so that it may
072     * be re-created later.
073     * 
074     * @param ssoClass
075     *            the type of SSO
076     * @param SSO
077     *            the SSO instance
078     */
079    <T> void set(Class<T> ssoClass, T SSO);
080}