    001    // Copyright 2008, 2009 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.tapestry5.annotations;
    016
    017    import java.lang.annotation.*;
    018
    019    import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;
    020    import org.apache.tapestry5.ioc.annotations.UseWith;
    021
    022    /**
    023     * Indicates that a method should only be evaluated once and the result cached. All further calls to the method will
    024     * return the cached result. Note that this annotation is inheritence-safe; if a subclass calls a superclass method that
    025     * has \@Cached then the value the subclass method gets is the cached value.
    026     * <p/>
    027     * The watch parameter can be passed a binding expression which will be evaluated each time the method is called. The
    028     * method will then only be executed the first time it is called and after that only when the value of the binding
    029     * changes. This can be used, for instance, to have the method only evaluated once per iteration of a loop by setting
    030     * watch to the value or index of the loop.
    031     */
    032    @Target(ElementType.METHOD)
    033    @Retention(RetentionPolicy.RUNTIME)
    034    @Documented
    035    @UseWith({COMPONENT,MIXIN,PAGE})
    036    public @interface Cached
    037    {
    038        /**
    039         * The optional binding to watch (default binding prefix is "prop").
    040         */
    041        String watch() default "";
    042    }