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}