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     */
017    package org.apache.commons.collections;
018    
019    import java.util.Collection;
020    import java.util.Iterator;
021    import java.util.Map;
022    
023    import org.apache.commons.collections.functors.ChainedTransformer;
024    import org.apache.commons.collections.functors.CloneTransformer;
025    import org.apache.commons.collections.functors.ClosureTransformer;
026    import org.apache.commons.collections.functors.ConstantTransformer;
027    import org.apache.commons.collections.functors.EqualPredicate;
028    import org.apache.commons.collections.functors.ExceptionTransformer;
029    import org.apache.commons.collections.functors.FactoryTransformer;
030    import org.apache.commons.collections.functors.InstantiateTransformer;
031    import org.apache.commons.collections.functors.InvokerTransformer;
032    import org.apache.commons.collections.functors.MapTransformer;
033    import org.apache.commons.collections.functors.NOPTransformer;
034    import org.apache.commons.collections.functors.PredicateTransformer;
035    import org.apache.commons.collections.functors.StringValueTransformer;
036    import org.apache.commons.collections.functors.SwitchTransformer;
037    
038    /**
039     * <code>TransformerUtils</code> provides reference implementations and 
040     * utilities for the Transformer functor interface. The supplied transformers are:
041     * <ul>
042     * <li>Invoker - returns the result of a method call on the input object
043     * <li>Clone - returns a clone of the input object
044     * <li>Constant - always returns the same object
045     * <li>Closure - performs a Closure and returns the input object
046     * <li>Predicate - returns the result of the predicate as a Boolean
047     * <li>Factory - returns a new object from a factory
048     * <li>Chained - chains two or more transformers together
049     * <li>Switch - calls one transformer based on one or more predicates
050     * <li>SwitchMap - calls one transformer looked up from a Map
051     * <li>Instantiate - the Class input object is instantiated
052     * <li>Map - returns an object from a supplied Map
053     * <li>Null - always returns null
054     * <li>NOP - returns the input object, which should be immutable
055     * <li>Exception - always throws an exception
056     * <li>StringValue - returns a <code>java.lang.String</code> representation of the input object
057     * </ul>
058     * All the supplied transformers are Serializable.
059     *
060     * @since Commons Collections 3.0
061     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
062     * 
063     * @author Stephen Colebourne
064     * @author James Carman
065     */
066    public class TransformerUtils {
067    
068        /**
069         * This class is not normally instantiated.
070         */
071        public TransformerUtils() {
072            super();
073        }
074    
075        /**
076         * Gets a transformer that always throws an exception.
077         * This could be useful during testing as a placeholder.
078         * 
079         * @see org.apache.commons.collections.functors.ExceptionTransformer
080         * 
081         * @return the transformer
082         */
083        public static Transformer exceptionTransformer() {
084            return ExceptionTransformer.INSTANCE;
085        }
086    
087        /**
088         * Gets a transformer that always returns null.
089         * 
090         * @see org.apache.commons.collections.functors.ConstantTransformer
091         * 
092         * @return the transformer
093         */
094        public static Transformer nullTransformer() {
095            return ConstantTransformer.NULL_INSTANCE;
096        }
097    
098        /**
099         * Gets a transformer that returns the input object.
100         * The input object should be immutable to maintain the
101         * contract of Transformer (although this is not checked).
102         * 
103         * @see org.apache.commons.collections.functors.NOPTransformer
104         * 
105         * @return the transformer
106         */
107        public static Transformer nopTransformer() {
108            return NOPTransformer.INSTANCE;
109        }
110    
111        /**
112         * Gets a transformer that returns a clone of the input
113         * object. The input object will be cloned using one of these
114         * techniques (in order):
115         * <ul>
116         * <li>public clone method
117         * <li>public copy constructor
118         * <li>serialization clone
119         * <ul>
120         * 
121         * @see org.apache.commons.collections.functors.CloneTransformer
122         * 
123         * @return the transformer
124         */
125        public static Transformer cloneTransformer() {
126            return CloneTransformer.INSTANCE;
127        }
128    
129        /**
130         * Creates a Transformer that will return the same object each time the 
131         * transformer is used.
132         *
133         * @see org.apache.commons.collections.functors.ConstantTransformer
134         * 
135         * @param constantToReturn  the constant object to return each time in the transformer
136         * @return the transformer.
137         */
138        public static Transformer constantTransformer(Object constantToReturn) {
139            return ConstantTransformer.getInstance(constantToReturn);
140        }
141    
142        /**
143         * Creates a Transformer that calls a Closure each time the transformer is used.
144         * The transformer returns the input object.
145         *
146         * @see org.apache.commons.collections.functors.ClosureTransformer
147         * 
148         * @param closure  the closure to run each time in the transformer, not null
149         * @return the transformer
150         * @throws IllegalArgumentException if the closure is null
151         */
152        public static Transformer asTransformer(Closure closure) {
153            return ClosureTransformer.getInstance(closure);
154        }
155    
156        /**
157         * Creates a Transformer that calls a Predicate each time the transformer is used.
158         * The transformer will return either Boolean.TRUE or Boolean.FALSE.
159         *
160         * @see org.apache.commons.collections.functors.PredicateTransformer
161         * 
162         * @param predicate  the predicate to run each time in the transformer, not null
163         * @return the transformer
164         * @throws IllegalArgumentException if the predicate is null
165         */
166        public static Transformer asTransformer(Predicate predicate) {
167            return PredicateTransformer.getInstance(predicate);
168        }
169    
170        /**
171         * Creates a Transformer that calls a Factory each time the transformer is used.
172         * The transformer will return the value returned by the factory.
173         *
174         * @see org.apache.commons.collections.functors.FactoryTransformer
175         * 
176         * @param factory  the factory to run each time in the transformer, not null
177         * @return the transformer
178         * @throws IllegalArgumentException if the factory is null
179         */
180        public static Transformer asTransformer(Factory factory) {
181            return FactoryTransformer.getInstance(factory);
182        }
183    
184        /**
185         * Create a new Transformer that calls two transformers, passing the result of
186         * the first into the second.
187         * 
188         * @see org.apache.commons.collections.functors.ChainedTransformer
189         * 
190         * @param transformer1  the first transformer
191         * @param transformer2  the second transformer
192         * @return the transformer
193         * @throws IllegalArgumentException if either transformer is null
194         */
195        public static Transformer chainedTransformer(Transformer transformer1, Transformer transformer2) {
196            return ChainedTransformer.getInstance(transformer1, transformer2);
197        }
198    
199        /**
200         * Create a new Transformer that calls each transformer in turn, passing the 
201         * result into the next transformer.
202         * 
203         * @see org.apache.commons.collections.functors.ChainedTransformer
204         * 
205         * @param transformers  an array of transformers to chain
206         * @return the transformer
207         * @throws IllegalArgumentException if the transformers array is null
208         * @throws IllegalArgumentException if any transformer in the array is null
209         */
210        public static Transformer chainedTransformer(Transformer[] transformers) {
211            return ChainedTransformer.getInstance(transformers);
212        }
213    
214        /**
215         * Create a new Transformer that calls each transformer in turn, passing the 
216         * result into the next transformer. The ordering is that of the iterator()
217         * method on the collection.
218         * 
219         * @see org.apache.commons.collections.functors.ChainedTransformer
220         * 
221         * @param transformers  a collection of transformers to chain
222         * @return the transformer
223         * @throws IllegalArgumentException if the transformers collection is null
224         * @throws IllegalArgumentException if any transformer in the collection is null
225         */
226        public static Transformer chainedTransformer(Collection transformers) {
227            return ChainedTransformer.getInstance(transformers);
228        }
229    
230        /**
231         * Create a new Transformer that calls one of two transformers depending 
232         * on the specified predicate.
233         * 
234         * @see org.apache.commons.collections.functors.SwitchTransformer
235         * 
236         * @param predicate  the predicate to switch on
237         * @param trueTransformer  the transformer called if the predicate is true
238         * @param falseTransformer  the transformer called if the predicate is false
239         * @return the transformer
240         * @throws IllegalArgumentException if the predicate is null
241         * @throws IllegalArgumentException if either transformer is null
242         */
243        public static Transformer switchTransformer(Predicate predicate, Transformer trueTransformer, Transformer falseTransformer) {
244            return SwitchTransformer.getInstance(new Predicate[] { predicate }, new Transformer[] { trueTransformer }, falseTransformer);
245        }
246    
247        /**
248         * Create a new Transformer that calls one of the transformers depending 
249         * on the predicates. The transformer at array location 0 is called if the
250         * predicate at array location 0 returned true. Each predicate is evaluated
251         * until one returns true. If no predicates evaluate to true, null is returned.
252         * 
253         * @see org.apache.commons.collections.functors.SwitchTransformer
254         * 
255         * @param predicates  an array of predicates to check
256         * @param transformers  an array of transformers to call
257         * @return the transformer
258         * @throws IllegalArgumentException if the either array is null
259         * @throws IllegalArgumentException if the either array has 0 elements
260         * @throws IllegalArgumentException if any element in the arrays is null
261         * @throws IllegalArgumentException if the arrays are different sizes
262         */
263        public static Transformer switchTransformer(Predicate[] predicates, Transformer[] transformers) {
264            return SwitchTransformer.getInstance(predicates, transformers, null);
265        }
266    
267        /**
268         * Create a new Transformer that calls one of the transformers depending 
269         * on the predicates. The transformer at array location 0 is called if the
270         * predicate at array location 0 returned true. Each predicate is evaluated
271         * until one returns true. If no predicates evaluate to true, the default
272         * transformer is called. If the default transformer is null, null is returned.
273         * 
274         * @see org.apache.commons.collections.functors.SwitchTransformer
275         * 
276         * @param predicates  an array of predicates to check
277         * @param transformers  an array of transformers to call
278         * @param defaultTransformer  the default to call if no predicate matches, null means return null
279         * @return the transformer
280         * @throws IllegalArgumentException if the either array is null
281         * @throws IllegalArgumentException if the either array has 0 elements
282         * @throws IllegalArgumentException if any element in the arrays is null
283         * @throws IllegalArgumentException if the arrays are different sizes
284         */
285        public static Transformer switchTransformer(Predicate[] predicates, Transformer[] transformers, Transformer defaultTransformer) {
286            return SwitchTransformer.getInstance(predicates, transformers, defaultTransformer);
287        }
288    
289        /**
290         * Create a new Transformer that calls one of the transformers depending 
291         * on the predicates. 
292         * <p>
293         * The Map consists of Predicate keys and Transformer values. A transformer 
294         * is called if its matching predicate returns true. Each predicate is evaluated
295         * until one returns true. If no predicates evaluate to true, the default
296         * transformer is called. The default transformer is set in the map with a 
297         * null key. If no default transformer is set, null will be returned in a default
298         * case. The ordering is that of the iterator() method on the entryset collection 
299         * of the map.
300         * 
301         * @see org.apache.commons.collections.functors.SwitchTransformer
302         * 
303         * @param predicatesAndTransformers  a map of predicates to transformers
304         * @return the transformer
305         * @throws IllegalArgumentException if the map is null
306         * @throws IllegalArgumentException if the map is empty
307         * @throws IllegalArgumentException if any transformer in the map is null
308         * @throws ClassCastException  if the map elements are of the wrong type
309         */
310        public static Transformer switchTransformer(Map predicatesAndTransformers) {
311            return SwitchTransformer.getInstance(predicatesAndTransformers);
312        }
313    
314        /**
315         * Create a new Transformer that uses the input object as a key to find the
316         * transformer to call. 
317         * <p>
318         * The Map consists of object keys and Transformer values. A transformer 
319         * is called if the input object equals the key. If there is no match, the
320         * default transformer is called. The default transformer is set in the map
321         * using a null key. If no default is set, null will be returned in a default case.
322         * 
323         * @see org.apache.commons.collections.functors.SwitchTransformer
324         * 
325         * @param objectsAndTransformers  a map of objects to transformers
326         * @return the transformer
327         * @throws IllegalArgumentException if the map is null
328         * @throws IllegalArgumentException if the map is empty
329         * @throws IllegalArgumentException if any transformer in the map is null
330         */
331        public static Transformer switchMapTransformer(Map objectsAndTransformers) {
332            Transformer[] trs = null;
333            Predicate[] preds = null;
334            if (objectsAndTransformers == null) {
335                throw new IllegalArgumentException("The object and transformer map must not be null");
336            }
337            Transformer def = (Transformer) objectsAndTransformers.remove(null);
338            int size = objectsAndTransformers.size();
339            trs = new Transformer[size];
340            preds = new Predicate[size];
341            int i = 0;
342            for (Iterator it = objectsAndTransformers.entrySet().iterator(); it.hasNext();) {
343                Map.Entry entry = (Map.Entry) it.next();
344                preds[i] = EqualPredicate.getInstance(entry.getKey());
345                trs[i] = (Transformer) entry.getValue();
346                i++;
347            }
348            return switchTransformer(preds, trs, def);
349        }
350    
351        /**
352         * Gets a Transformer that expects an input Class object that it will instantiate.
353         * 
354         * @see org.apache.commons.collections.functors.InstantiateTransformer
355         * 
356         * @return the transformer
357         */
358        public static Transformer instantiateTransformer() {
359            return InstantiateTransformer.NO_ARG_INSTANCE;
360        }
361    
362        /** 
363         * Creates a Transformer that expects an input Class object that it will 
364         * instantiate. The constructor used is determined by the arguments specified
365         * to this method.
366         *
367         * @see org.apache.commons.collections.functors.InstantiateTransformer
368         * 
369         * @param paramTypes  parameter types for the constructor, can be null
370         * @param args  the arguments to pass to the constructor, can be null
371         * @return the transformer
372         * @throws IllegalArgumentException if the paramTypes and args don't match
373         */
374        public static Transformer instantiateTransformer(Class[] paramTypes, Object[] args) {
375            return InstantiateTransformer.getInstance(paramTypes, args);
376        }
377    
378        /** 
379         * Creates a Transformer that uses the passed in Map to transform the input 
380         * object (as a simple lookup).
381         *
382         * @see org.apache.commons.collections.functors.MapTransformer
383         * 
384         * @param map  the map to use to transform the objects
385         * @return the transformer
386         * @throws IllegalArgumentException if the map is null
387         */
388        public static Transformer mapTransformer(Map map) {
389            return MapTransformer.getInstance(map);
390        }
391    
392        /**
393         * Gets a Transformer that invokes a method on the input object.
394         * The method must have no parameters. If the input object is null, 
395         * null is returned.
396         * <p>
397         * For example, <code>TransformerUtils.invokerTransformer("getName");</code>
398         * will call the <code>getName/code> method on the input object to 
399         * determine the transformer result.
400         * 
401         * @see org.apache.commons.collections.functors.InvokerTransformer
402         * 
403         * @param methodName  the method name to call on the input object, may not be null
404         * @return the transformer
405         * @throws IllegalArgumentException if the methodName is null.
406         */
407        public static Transformer invokerTransformer(String methodName){
408            return InvokerTransformer.getInstance(methodName, null, null);
409        }
410    
411        /**
412         * Gets a Transformer that invokes a method on the input object.
413         * The method parameters are specified. If the input object is null, 
414         * null is returned.
415         * 
416         * @see org.apache.commons.collections.functors.InvokerTransformer
417         * 
418         * @param methodName  the name of the method
419         * @param paramTypes  the parameter types
420         * @param args  the arguments
421         * @return the transformer
422         * @throws IllegalArgumentException if the method name is null
423         * @throws IllegalArgumentException if the paramTypes and args don't match
424         */
425        public static Transformer invokerTransformer(String methodName, Class[] paramTypes, Object[] args){
426            return InvokerTransformer.getInstance(methodName, paramTypes, args);
427        }
428    
429        /**
430         * Gets a transformer that returns a <code>java.lang.String</code>
431         * representation of the input object. This is achieved via the
432         * <code>toString</code> method, <code>null</code> returns 'null'.
433         * 
434         * @see org.apache.commons.collections.functors.StringValueTransformer
435         * 
436         * @return the transformer
437         */
438        public static Transformer stringValueTransformer() {
439            return StringValueTransformer.INSTANCE;
440        }
441        
442    }