1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.collections4; 18 19 import org.apache.commons.collections4.functors.ConstantFactory; 20 import org.apache.commons.collections4.functors.ExceptionFactory; 21 import org.apache.commons.collections4.functors.InstantiateFactory; 22 import org.apache.commons.collections4.functors.PrototypeFactory; 23 24 /** 25 * {@code FactoryUtils} provides reference implementations and utilities 26 * for the Factory functor interface. The supplied factories are: 27 * <ul> 28 * <li>Prototype - clones a specified object 29 * <li>Instantiate - creates objects using reflection 30 * <li>Constant - always returns the same object 31 * <li>Null - always returns null 32 * <li>Exception - always throws an exception 33 * </ul> 34 * <p> 35 * Since v4.1 only factories which are considered to be safe are 36 * Serializable. Factories considered to be unsafe for serialization are: 37 * <ul> 38 * <li>Prototype 39 * <li>Instantiate 40 * </ul> 41 * 42 * @since 3.0 43 */ 44 public class FactoryUtils { 45 46 /** 47 * Creates a Factory that will return the same object each time the factory 48 * is used. No check is made that the object is immutable. In general, only 49 * immutable objects should use the constant factory. Mutable objects should 50 * use the prototype factory. 51 * 52 * @see org.apache.commons.collections4.functors.ConstantFactory 53 * 54 * @param <T> the type that the factory creates 55 * @param constantToReturn the constant object to return each time in the factory 56 * @return the {@code constant} factory. 57 */ 58 public static <T> Factory<T> constantFactory(final T constantToReturn) { 59 return ConstantFactory.constantFactory(constantToReturn); 60 } 61 62 /** 63 * Gets a Factory that always throws an exception. 64 * This could be useful during testing as a placeholder. 65 * 66 * @see org.apache.commons.collections4.functors.ExceptionFactory 67 * 68 * @param <T> the type that the factory creates 69 * @return the factory 70 */ 71 public static <T> Factory<T> exceptionFactory() { 72 return ExceptionFactory.<T>exceptionFactory(); 73 } 74 75 /** 76 * Creates a Factory that can create objects of a specific type using 77 * a no-args constructor. 78 * 79 * @see org.apache.commons.collections4.functors.InstantiateFactory 80 * 81 * @param <T> the type that the factory creates 82 * @param classToInstantiate the Class to instantiate each time in the factory 83 * @return the {@code reflection} factory 84 * @throws NullPointerException if the classToInstantiate is null 85 */ 86 public static <T> Factory<T> instantiateFactory(final Class<T> classToInstantiate) { 87 return InstantiateFactory.instantiateFactory(classToInstantiate, null, null); 88 } 89 90 /** 91 * Creates a Factory that can create objects of a specific type using 92 * the arguments specified to this method. 93 * 94 * @see org.apache.commons.collections4.functors.InstantiateFactory 95 * 96 * @param <T> the type that the factory creates 97 * @param classToInstantiate the Class to instantiate each time in the factory 98 * @param paramTypes parameter types for the constructor, can be null 99 * @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 }