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    
015    package org.apache.tapestry5.annotations;
016    
017    import org.apache.tapestry5.services.Session;
018    
019    import java.lang.annotation.Documented;
020    import static java.lang.annotation.ElementType.FIELD;
021    import java.lang.annotation.Retention;
022    import static java.lang.annotation.RetentionPolicy.RUNTIME;
023    import java.lang.annotation.Target;
024    
025    import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;
026    import 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})
049    public @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    }