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}