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}