    001// Copyright 2009 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.annotations;
    016
    017import java.lang.annotation.Documented;
    018import static java.lang.annotation.ElementType.FIELD;
    019import java.lang.annotation.Retention;
    020import static java.lang.annotation.RetentionPolicy.RUNTIME;
    021import java.lang.annotation.Target;
    022
    023import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;
    024import org.apache.tapestry5.ioc.annotations.UseWith;
    025
    026/**
    027 * Marker annotation for a field that is a <em>session state object</em> (SSO) as controlled by the {@link
    028 * org.apache.tapestry5.services.ApplicationStateManager}. An SSO stored as global session object (i.e., in the {@link
    029 * javax.servlet.ServletContext}); every page or component. In fact, the built-in strategies for ASO management are
    030 * <em>very</em> user specific, ultimately storing data in the {@link org.apache.tapestry5.services.Session}.
    031 * <p/>
    032 * An SSO field may have a companion field, of type boolean, used to see if the SSO has been created yet. If another
    033 * field exists with the same name, suffixed with "Exists" (i.e., "sso" for the SSO field, and "ssoExists" for the
    034 * companion field) and the type of that field is boolean, then access to the field will determine whether the SSO has
    035 * already been created. This is necessary because even a null check ("sso != null") may force the SSO to be created.
    036 * Instead, check the companion boolean field ("asoExists").
    037 * <p/>
    038 * Note: Tapestry 5.0 called these objects "Application State Objects"; thus many of the underlying services have a
    039 * confusing name (ApplicationStateManager, which really should be SessionStateManager ... but can't be renamed for
    040 * backwards compatibility reasons).
    041 *
    042 * @since 5.1.0.4
    043 */
    044@Target(FIELD)
    045@Documented
    046@Retention(RUNTIME)
    047@UseWith({COMPONENT,MIXIN,PAGE})
    048public @interface SessionState
    049{
    050    /**
    051     * If true (the default), then referencing an field marked with the annotation will create the SSO.  If false, then
    052     * accessing the field will not create the SSO, it will only allow access to it if it already exists.
    053     */
    054    boolean create() default true;
    055}