001    // Copyright 2006 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.tapestry.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    /**
024     * Marker annotation placed on fields whose value should be retained past the end of the request. This is most often
025     * associated with fields that are <em>lazily loaded</em>. By marking such fields with the Retain annotation, the fields
026     * will <em>not</em> be discarded at the end of the request.
027     * <p/>
028     * This is quite different from {@link Persist}, because the value that's allowed to be retained is not stored
029     * persistently; it is simply not cleared out. A subsequent request, even from the same user, may be processed by a
030     * different instance of the page where the value is still null.
031     * <p/>
032     * This annotation should only be used with lazily-evaluated objects that contain no client-specific information.
033     */
034    @Target(FIELD)
035    @Retention(RUNTIME)
036    @Documented
037    public @interface Retain
038    {
039    
040    }