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
015package org.apache.tapestry5.annotations;
016
017import java.lang.annotation.*;
018
019import static org.apache.tapestry5.ioc.annotations.AnnotationUseContext.*;
020import 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})
036public @interface Cached
037{
038    /**
039     * The optional binding to watch (default binding prefix is "prop").
040     */
041    String watch() default "";
042}