001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.commons.collections4; 018 019import org.apache.commons.collections4.functors.ConstantFactory; 020import org.apache.commons.collections4.functors.ExceptionFactory; 021import org.apache.commons.collections4.functors.InstantiateFactory; 022import org.apache.commons.collections4.functors.PrototypeFactory; 023 024/** 025 * {@code FactoryUtils} provides reference implementations and utilities 026 * for the Factory functor interface. The supplied factories are: 027 * <ul> 028 * <li>Prototype - clones a specified object 029 * <li>Instantiate - creates objects using reflection 030 * <li>Constant - always returns the same object 031 * <li>Null - always returns null 032 * <li>Exception - always throws an exception 033 * </ul> 034 * <p> 035 * Since v4.1 only factories which are considered to be safe are 036 * Serializable. Factories considered to be unsafe for serialization are: 037 * <ul> 038 * <li>Prototype 039 * <li>Instantiate 040 * </ul> 041 * 042 * @since 3.0 043 */ 044public class FactoryUtils { 045 046 /** 047 * Creates a Factory that will return the same object each time the factory 048 * is used. No check is made that the object is immutable. In general, only 049 * immutable objects should use the constant factory. Mutable objects should 050 * use the prototype factory. 051 * 052 * @see org.apache.commons.collections4.functors.ConstantFactory 053 * 054 * @param <T> the type that the factory creates 055 * @param constantToReturn the constant object to return each time in the factory 056 * @return the {@code constant} factory. 057 */ 058 public static <T> Factory<T> constantFactory(final T constantToReturn) { 059 return ConstantFactory.constantFactory(constantToReturn); 060 } 061 062 /** 063 * Gets a Factory that always throws an exception. 064 * This could be useful during testing as a placeholder. 065 * 066 * @see org.apache.commons.collections4.functors.ExceptionFactory 067 * 068 * @param <T> the type that the factory creates 069 * @return the factory 070 */ 071 public static <T> Factory<T> exceptionFactory() { 072 return ExceptionFactory.<T>exceptionFactory(); 073 } 074 075 /** 076 * Creates a Factory that can create objects of a specific type using 077 * a no-args constructor. 078 * 079 * @see org.apache.commons.collections4.functors.InstantiateFactory 080 * 081 * @param <T> the type that the factory creates 082 * @param classToInstantiate the Class to instantiate each time in the factory 083 * @return the {@code reflection} factory 084 * @throws NullPointerException if the classToInstantiate is null 085 */ 086 public static <T> Factory<T> instantiateFactory(final Class<T> classToInstantiate) { 087 return InstantiateFactory.instantiateFactory(classToInstantiate, null, null); 088 } 089 090 /** 091 * Creates a Factory that can create objects of a specific type using 092 * the arguments specified to this method. 093 * 094 * @see org.apache.commons.collections4.functors.InstantiateFactory 095 * 096 * @param <T> the type that the factory creates 097 * @param classToInstantiate the Class to instantiate each time in the factory 098 * @param paramTypes parameter types for the constructor, can be null 099 * @param args the arguments to pass to the constructor, can be null 100 * @return the {@code reflection} factory 101 * @throws NullPointerException if the classToInstantiate is null 102 * @throws IllegalArgumentException if the paramTypes and args don't match 103 * @throws IllegalArgumentException if the constructor doesn't exist 104 */ 105 public static <T> Factory<T> instantiateFactory(final Class<T> classToInstantiate, final Class<?>[] paramTypes, 106 final Object[] args) { 107 return InstantiateFactory.instantiateFactory(classToInstantiate, paramTypes, args); 108 } 109 110 /** 111 * Gets a Factory that will return null each time the factory is used. 112 * This could be useful during testing as a placeholder. 113 * 114 * @see org.apache.commons.collections4.functors.ConstantFactory 115 * @param <T> the "type" of null object the factory should return. 116 * @return the factory 117 */ 118 public static <T> Factory<T> nullFactory() { 119 return ConstantFactory.<T>constantFactory(null); 120 } 121 122 /** 123 * Creates a Factory that will return a clone of the same prototype object 124 * each time the factory is used. The prototype will be cloned using one of these 125 * techniques (in order): 126 * 127 * <ul> 128 * <li>public clone method</li> 129 * <li>public copy constructor</li> 130 * <li>serialization clone</li> 131 * </ul> 132 * 133 * @see org.apache.commons.collections4.functors.PrototypeFactory 134 * 135 * @param <T> the type that the factory creates 136 * @param prototype the object to clone each time in the factory 137 * @return the {@code prototype} factory, or a {@link ConstantFactory#NULL_INSTANCE} if 138 * the {@code prototype} is {@code null} 139 * @throws IllegalArgumentException if the prototype cannot be cloned 140 */ 141 public static <T> Factory<T> prototypeFactory(final T prototype) { 142 return PrototypeFactory.<T>prototypeFactory(prototype); 143 } 144 145 /** 146 * Don't allow instances. 147 */ 148 private FactoryUtils() { 149 // empty 150 } 151 152}