    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
    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 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 })
    046public @interface Retain
    047{
    048
    049}