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
150 }