001// Copyright 2006, 2007, 2008, 2009, 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.annotations;
016
017import org.apache.tapestry5.services.Session;
018
019import java.lang.annotation.Documented;
020import static java.lang.annotation.ElementType.FIELD;
021import java.lang.annotation.Retention;
022import static java.lang.annotation.RetentionPolicy.RUNTIME;
023import java.lang.annotation.Target;
024
025import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;
026import org.apache.tapestry5.ioc.annotations.UseWith;
027
028/**
029 * Identifies a field as persistent, meaning its value persists from one request to the next. Different strategies exist
030 * for how this is accomplished, the most common being the default, "session", which stores the field's value in the
031 * {@link Session}.
032 * <p/>
033 * In most cases, the value will be omitted and will default to the empty string. This forces a search for the correct
034 * strategy. Starting with the component (or mixin) itself, a check is made for the {@link Meta meta data property}
035 * <code>tapestry.persistence-strategy</code>. If a value is found, it is used, otherwise the search continues up the
036 * inheritance hierarchy, towards the page. If not found, then the "session" strategy is used.
037 * <p/>
038 * In this way, the session persistence strategy for a component and all of its sub-components can be controlled by the
039 * containing component.
040 *
041 * @see org.apache.tapestry5.services.MetaDataLocator
042 * @see org.apache.tapestry5.PersistenceConstants
043 * @see ActivationRequestParameter
044 */
045@Target(FIELD)
046@Documented
047@Retention(RUNTIME)
048@UseWith({COMPONENT,MIXIN,PAGE})
049public @interface Persist
050{
051
052    /**
053     * The strategy used to persist the value. The default value, the empty string, allows persistence to be decided by
054     * the containing component and component hierarchy.
055     */
056    String value() default "";
057}