001// *************************************************************************************************************************** 002// * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file * 003// * distributed with this work for additional information regarding copyright ownership. The ASF licenses this file * 004// * to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance * 005// * with the License. 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 distributed under the License is distributed on an * 010// * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the * 011// * specific language governing permissions and limitations under the License. * 012// *************************************************************************************************************************** 013package org.apache.juneau.annotation; 014 015import static java.lang.annotation.ElementType.*; 016import static java.lang.annotation.RetentionPolicy.*; 017 018import java.lang.annotation.*; 019 020import org.apache.juneau.*; 021 022/** 023 * Maps constructor arguments to property names on beans with read-only properties. 024 * 025 * <p> 026 * This annotation can be used in the case of beans with properties whose values can only be set by passing them in 027 * through a constructor on the class. 028 * <br>Since method parameter names are lost during compilation, this annotation essentially redefines them so that they 029 * are available at runtime. 030 * 031 * <p> 032 * This annotation can only be applied to constructors and can only be applied to one constructor per class. 033 * 034 * <p> 035 * When present, bean instantiation is delayed until the call to {@link BeanMap#getBean()}. 036 * Until then, bean property values are stored in a local cache until <c>getBean()</c> is called. 037 * Because of this additional caching step, parsing into read-only beans tends to be slower and use more memory than 038 * parsing into beans with writable properties. 039 * 040 * <p> 041 * Attempting to call {@link BeanMap#put(String,Object)} on a read-only property after calling {@link BeanMap#getBean()} 042 * will result in a {@link BeanRuntimeException} being thrown. 043 * Multiple calls to {@link BeanMap#getBean()} will return the same bean instance. 044 * 045 * <ul class='seealso'> 046 * <li class='link'>{@doc juneau-marshall.Transforms.BeanConstructorAnnotation} 047 * </ul> 048 */ 049@Documented 050@Target(CONSTRUCTOR) 051@Retention(RUNTIME) 052@Inherited 053public @interface BeanConstructor { 054 055 /** 056 * The names of the properties of the constructor arguments. 057 * <p> 058 * The {@link org.apache.juneau.annotation.BeanConstructor @BeanConstructor} annotation is used to 059 * map constructor arguments to property names on bean with read-only properties. 060 * <br>Since method parameter names are lost during compilation, this annotation essentially redefines 061 * them so that they are available at runtime. 062 * </p> 063 * <p> 064 * The definition of a read-only bean is a bean with properties with only getters, like shown below: 065 * </p> 066 * <p class='bpcode w800'> 067 * <jc>// Our read-only bean.</jc> 068 * <jk>public class</jk> Person { 069 * <jk>private final</jk> String <jf>name</jf>; 070 * <jk>private final int</jk> <jf>age</jf>; 071 * 072 * <ja>@BeanConstructor</ja>(properties=<js>"name,age"</js>) 073 * <jk>public</jk> Person(String name, <jk>int</jk> age) { 074 * <jk>this</jk>.<jf>name</jf> = name; 075 * <jk>this</jk>.<jf>age</jf> = age; 076 * } 077 * 078 * <jc>// Read only properties.</jc> 079 * <jc>// Getters, but no setters.</jc> 080 * 081 * <jk>public</jk> String getName() { 082 * <jk>return</jk> <jf>name</jf>; 083 * } 084 * 085 * <jk>public int</jk> getAge() { 086 * <jk>return</jk> <jf>age</jf>; 087 * } 088 * } 089 * </p> 090 * <p class='bpcode w800'> 091 * <jc>// Parsing into a read-only bean.</jc> 092 * String json = <js>"{name:'John Smith',age:45}"</js>; 093 * Person p = JsonParser.<jsf>DEFAULT</jsf>.parse(json); 094 * String name = p.getName(); <jc>// "John Smith"</jc> 095 * <jk>int</jk> age = p.getAge(); <jc>// 45</jc> 096 * </p> 097 * <p> 098 * Note that the {@link Name @Name} annotation can also be used to identify bean property names on constructor 099 * arguments. If neither this annotation or {@link Name @Name} is used, then we try to get the property names 100 * from the parameter names if they are available in the bytecode. 101 * </p> 102 */ 103 String properties() default ""; 104}