    001    // Copyright 2006, 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 java.lang.annotation.Documented;
    018    import static java.lang.annotation.ElementType.FIELD;
    019    import java.lang.annotation.Retention;
    020    import static java.lang.annotation.RetentionPolicy.RUNTIME;
    021    import java.lang.annotation.Target;
    022
    023    import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;
    024    import org.apache.tapestry5.ioc.annotations.UseWith;
    025
    026    /**
    027     * Marker annotation placed on fields whose value should be retained past the end of the request. This is most often
    028     * associated with fields that are <em>lazily loaded</em>. By marking such fields with the Retain annotation, the fields
    029     * will <em>not</em> be discarded at the end of the request.
    030     * <p/>
    031     * This is quite different from {@link Persist}, because the value that's allowed to be retained is not stored
    032     * persistently; it is simply not cleared out. A subsequent request, even from the same user, may be processed by a
    033     * different instance of the page where the value is still null.
    034     * <p/>
    035     * This annotation should only be used with lazily-evaluated objects that contain no client-specific information.
    036     *
    037     * @deprecated This rarely used annotation is likely to cause threading issues starting in Tapestry 5.2 (which no longer
    038     *             pools pages
    039     *             but uses shared instances with externalized mutable state)
    040     */
    041    @Target(FIELD)
    042    @Retention(RUNTIME)
    043    @Documented
    044    @UseWith(
    045    { COMPONENT, MIXIN, PAGE })
    046    public @interface Retain
    047    {
    048
    049    }