    001// Licensed under the Apache License, Version 2.0 (the "License");
    002// you may not use this file except in compliance with the License.
    003// You may obtain a copy of the License at
    004//
    005// http://www.apache.org/licenses/LICENSE-2.0
    006//
    007// Unless required by applicable law or agreed to in writing, software
    008// distributed under the License is distributed on an "AS IS" BASIS,
    009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    010// See the License for the specific language governing permissions and
    011// limitations under the License.
    012
    013package org.apache.tapestry5.annotations;
    014
    015import org.apache.tapestry5.ioc.annotations.UseWith;
    016
    017import java.lang.annotation.Documented;
    018import java.lang.annotation.Retention;
    019import java.lang.annotation.Target;
    020
    021import static java.lang.annotation.ElementType.FIELD;
    022import static java.lang.annotation.RetentionPolicy.RUNTIME;
    023import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;
    024
    025/**
    026 * Marker annotation placed on fields whose value should be retained past the end of the request. This is most often
    027 * associated with fields that are <em>lazily loaded</em>. By marking such fields with the Retain annotation, the fields
    028 * will <em>not</em> be discarded at the end of the request.
    029 *
    030 * This is quite different from {@link Persist}, because the value that's allowed to be retained is not stored
    031 * persistently; it is simply not cleared out. A subsequent request, even from the same user, may be processed by a
    032 * different instance of the page where the value is still null.
    033 *
    034 * This annotation should only be used with lazily-evaluated objects that contain no client-specific information.
    035 *
    036 * @deprecated This rarely used annotation is likely to cause threading issues starting in Tapestry 5.2 (which no longer
    037 *             pools pages
    038 *             but uses shared instances with externalized mutable state)
    039 */
    040@Target(FIELD)
    041@Retention(RUNTIME)
    042@Documented
    043@UseWith(
    044{ COMPONENT, MIXIN, PAGE })
    045public @interface Retain
    046{
    047
    048}