// Copyright 2007, 2008 The Apache Software Foundation

 //

 // Licensed under the Apache License, Version 2.0 (the "License");

 // you may not use this file except in compliance with the License.

 // You may obtain a copy of the License at

 //

 //     http://www.apache.org/licenses/LICENSE-2.0

 //

 // Unless required by applicable law or agreed to in writing, software

 // distributed under the License is distributed on an "AS IS" BASIS,

 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 // See the License for the specific language governing permissions and

 // limitations under the License.

 package org.apache.tapestry5.services;

 import org.apache.tapestry5.ioc.annotations.UsesMappedConfiguration;

 /**

  * Responsible for managing <em>session state objects</em>, objects which persist between requests, but are not tied to

  * any individual page or component. SSOs are also created on demand. SSOs are typically stored in the session, so that

  * they are specific to a particular client.

  * <p/>

  * The term "Application" is a hold-over from Tapestry 5.0, which used the {@link ApplicationState} annotation, and

  * called them "ASOs" (Application State Objects).

  * <p/>

  * Tapestry has a built-in default strategy for storing SSOs (in the session) and instantiating them. If desired,

  * contributions to the service configuration can override the default behavior, either specifying an alternate storage

  * strategy, or an alternate {@linkplain org.apache.tapestry5.services.ApplicationStateCreator creation strategy}.

  *

  * @see org.apache.tapestry5.annotations.ApplicationState

  */

 @UsesMappedConfiguration(key = Class.class, value = ApplicationStateContribution.class)

 public interface ApplicationStateManager

 {

     /**

      * For a given class, find the SSO for the class, creating it if necessary. The manager has a configuration that

      * determines how an instance is stored and created as needed. A requested SSO not in the configuration is assumed

      * to be created via a no-args constructor, and stored in the session.

      *

      * @param <T>

      * @param ssoClass identifies the SSO to access or create

      * @return the SSO instance

      */

     <T> T get(Class<T> ssoClass);

     /**

      * For a given class, find the SSO for the class. The manager has a configuration that determines how an instance is

      * stored.

      *

      * @param <T>

      * @param ssoClass identifies the SSO to access or create

      * @return the SSO instance or null if it does not already exist

      */

     <T> T getIfExists(Class<T> ssoClass);

     /**

      * Returns true if the SSO already exists, false if it has not yet been created.

      *

      * @param ssoClass used to select the SSO

      * @return true if SSO exists, false if null

      */

     <T> boolean exists(Class<T> ssoClass);

     /**

      * Stores a new SSO, replacing the existing SSO (if any). Storing the value null will delete the SSO so that it may

      * be re-created later.

      *

      * @param <T>

      * @param ssoClass the type of SSO

      * @param SSO      the SSO instance

      */

     <T> void set(Class<T> ssoClass, T SSO);

 }