TransformerUtils


1   /*
2    *  Copyright 2002-2004 The Apache Software Foundation
3    *
4    *  Licensed under the Apache License, Version 2.0 (the "License");
5    *  you may not use this file except in compliance with the License.
6    *  You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   *  Unless required by applicable law or agreed to in writing, software
11   *  distributed under the License is distributed on an "AS IS" BASIS,
12   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   *  See the License for the specific language governing permissions and
14   *  limitations under the License.
15   */
16  package org.apache.commons.collections;
17  
18  import java.util.Collection  ;
19  import java.util.Iterator  ;
20  import java.util.Map  ;
21  
22  import org.apache.commons.collections.functors.ChainedTransformer;
23  import org.apache.commons.collections.functors.CloneTransformer;
24  import org.apache.commons.collections.functors.ClosureTransformer;
25  import org.apache.commons.collections.functors.ConstantTransformer;
26  import org.apache.commons.collections.functors.EqualPredicate;
27  import org.apache.commons.collections.functors.ExceptionTransformer;
28  import org.apache.commons.collections.functors.FactoryTransformer;
29  import org.apache.commons.collections.functors.InstantiateTransformer;
30  import org.apache.commons.collections.functors.InvokerTransformer;
31  import org.apache.commons.collections.functors.MapTransformer;
32  import org.apache.commons.collections.functors.NOPTransformer;
33  import org.apache.commons.collections.functors.PredicateTransformer;
34  import org.apache.commons.collections.functors.StringValueTransformer;
35  import org.apache.commons.collections.functors.SwitchTransformer;
36  
37  /**
38   * <code>TransformerUtils</code> provides reference implementations and 
39   * utilities for the Transformer functor interface. The supplied transformers are:
40   * <ul>
41   * <li>Invoker - returns the result of a method call on the input object
42   * <li>Clone - returns a clone of the input object
43   * <li>Constant - always returns the same object
44   * <li>Closure - performs a Closure and returns the input object
45   * <li>Predicate - returns the result of the predicate as a Boolean
46   * <li>Factory - returns a new object from a factory
47   * <li>Chained - chains two or more transformers together
48   * <li>Switch - calls one transformer based on one or more predicates
49   * <li>SwitchMap - calls one transformer looked up from a Map
50   * <li>Instantiate - the Class input object is instantiated
51   * <li>Map - returns an object from a supplied Map
52   * <li>Null - always returns null
53   * <li>NOP - returns the input object, which should be immutable
54   * <li>Exception - always throws an exception
55   * <li>StringValue - returns a <code>java.lang.String</code> representation of the input object
56   * </ul>
57   * All the supplied transformers are Serializable.
58   *
59   * @since Commons Collections 3.0
60   * @version $Revision: 1.13 $ $Date: 2004/05/26 21:50:52 $
61   * 
62   * @author Stephen Colebourne
63   * @author James Carman
64   */
65  public class TransformerUtils {
66  
67      /**
68       * This class is not normally instantiated.
69       */
70      public TransformerUtils() {
71          super();
72      }
73  
74      /**
75       * Gets a transformer that always throws an exception.
76       * This could be useful during testing as a placeholder.
77       * 
78       * @see org.apache.commons.collections.functors.ExceptionTransformer
79       * 
80       * @return the transformer
81       */
82      public static Transformer exceptionTransformer() {
83          return ExceptionTransformer.INSTANCE;
84      }
85  
86      /**
87       * Gets a transformer that always returns null.
88       * 
89       * @see org.apache.commons.collections.functors.ConstantTransformer
90       * 
91       * @return the transformer
92       */
93      public static Transformer nullTransformer() {
94          return ConstantTransformer.NULL_INSTANCE;
95      }
96  
97      /**
98       * Gets a transformer that returns the input object.
99       * The input object should be immutable to maintain the
100      * contract of Transformer (although this is not checked).
101      * 
102      * @see org.apache.commons.collections.functors.NOPTransformer
103      * 
104      * @return the transformer
105      */
106     public static Transformer nopTransformer() {
107         return NOPTransformer.INSTANCE;
108     }
109 
110     /**
111      * Gets a transformer that returns a clone of the input
112      * object. The input object will be cloned using one of these
113      * techniques (in order):
114      * <ul>
115      * <li>public clone method
116      * <li>public copy constructor
117      * <li>serialization clone
118      * <ul>
119      * 
120      * @see org.apache.commons.collections.functors.CloneTransformer
121      * 
122      * @return the transformer
123      */
124     public static Transformer cloneTransformer() {
125         return CloneTransformer.INSTANCE;
126     }
127 
128     /**
129      * Creates a Transformer that will return the same object each time the 
130      * transformer is used.
131      *
132      * @see org.apache.commons.collections.functors.ConstantTransformer
133      * 
134      * @param constantToReturn  the constant object to return each time in the transformer
135      * @return the transformer.
136      */
137     public static Transformer constantTransformer(Object   constantToReturn) {
138         return ConstantTransformer.getInstance(constantToReturn);
139     }
140 
141     /**
142      * Creates a Transformer that calls a Closure each time the transformer is used.
143      * The transformer returns the input object.
144      *
145      * @see org.apache.commons.collections.functors.ClosureTransformer
146      * 
147      * @param closure  the closure to run each time in the transformer, not null
148      * @return the transformer
149      * @throws IllegalArgumentException if the closure is null
150      */
151     public static Transformer asTransformer(Closure closure) {
152         return ClosureTransformer.getInstance(closure);
153     }
154 
155     /**
156      * Creates a Transformer that calls a Predicate each time the transformer is used.
157      * The transformer will return either Boolean.TRUE or Boolean.FALSE.
158      *
159      * @see org.apache.commons.collections.functors.PredicateTransformer
160      * 
161      * @param predicate  the predicate to run each time in the transformer, not null
162      * @return the transformer
163      * @throws IllegalArgumentException if the predicate is null
164      */
165     public static Transformer asTransformer(Predicate predicate) {
166         return PredicateTransformer.getInstance(predicate);
167     }
168 
169     /**
170      * Creates a Transformer that calls a Factory each time the transformer is used.
171      * The transformer will return the value returned by the factory.
172      *
173      * @see org.apache.commons.collections.functors.FactoryTransformer
174      * 
175      * @param factory  the factory to run each time in the transformer, not null
176      * @return the transformer
177      * @throws IllegalArgumentException if the factory is null
178      */
179     public static Transformer asTransformer(Factory factory) {
180         return FactoryTransformer.getInstance(factory);
181     }
182 
183     /**
184      * Create a new Transformer that calls two transformers, passing the result of
185      * the first into the second.
186      * 
187      * @see org.apache.commons.collections.functors.ChainedTransformer
188      * 
189      * @param transformer1  the first transformer
190      * @param transformer2  the second transformer
191      * @return the transformer
192      * @throws IllegalArgumentException if either transformer is null
193      */
194     public static Transformer chainedTransformer(Transformer transformer1, Transformer transformer2) {
195         return ChainedTransformer.getInstance(transformer1, transformer2);
196     }
197 
198     /**
199      * Create a new Transformer that calls each transformer in turn, passing the 
200      * result into the next transformer.
201      * 
202      * @see org.apache.commons.collections.functors.ChainedTransformer
203      * 
204      * @param transformers  an array of transformers to chain
205      * @return the transformer
206      * @throws IllegalArgumentException if the transformers array is null
207      * @throws IllegalArgumentException if any transformer in the array is null
208      */
209     public static Transformer chainedTransformer(Transformer[] transformers) {
210         return ChainedTransformer.getInstance(transformers);
211     }
212 
213     /**
214      * Create a new Transformer that calls each transformer in turn, passing the 
215      * result into the next transformer. The ordering is that of the iterator()
216      * method on the collection.
217      * 
218      * @see org.apache.commons.collections.functors.ChainedTransformer
219      * 
220      * @param transformers  a collection of transformers to chain
221      * @return the transformer
222      * @throws IllegalArgumentException if the transformers collection is null
223      * @throws IllegalArgumentException if any transformer in the collection is null
224      */
225     public static Transformer chainedTransformer(Collection   transformers) {
226         return ChainedTransformer.getInstance(transformers);
227     }
228 
229     /**
230      * Create a new Transformer that calls one of two transformers depending 
231      * on the specified predicate.
232      * 
233      * @see org.apache.commons.collections.functors.SwitchTransformer
234      * 
235      * @param predicate  the predicate to switch on
236      * @param trueTransformer  the transformer called if the predicate is true
237      * @param falseTransformer  the transformer called if the predicate is false
238      * @return the transformer
239      * @throws IllegalArgumentException if the predicate is null
240      * @throws IllegalArgumentException if either transformer is null
241      */
242     public static Transformer switchTransformer(Predicate predicate, Transformer trueTransformer, Transformer falseTransformer) {
243         return SwitchTransformer.getInstance(new Predicate[] { predicate }, new Transformer[] { trueTransformer }, falseTransformer);
244     }
245 
246     /**
247      * Create a new Transformer that calls one of the transformers depending 
248      * on the predicates. The transformer at array location 0 is called if the
249      * predicate at array location 0 returned true. Each predicate is evaluated
250      * until one returns true. If no predicates evaluate to true, null is returned.
251      * 
252      * @see org.apache.commons.collections.functors.SwitchTransformer
253      * 
254      * @param predicates  an array of predicates to check
255      * @param transformers  an array of transformers to call
256      * @return the transformer
257      * @throws IllegalArgumentException if the either array is null
258      * @throws IllegalArgumentException if the either array has 0 elements
259      * @throws IllegalArgumentException if any element in the arrays is null
260      * @throws IllegalArgumentException if the arrays are different sizes
261      */
262     public static Transformer switchTransformer(Predicate[] predicates, Transformer[] transformers) {
263         return SwitchTransformer.getInstance(predicates, transformers, null);
264     }
265 
266     /**
267      * Create a new Transformer that calls one of the transformers depending 
268      * on the predicates. The transformer at array location 0 is called if the
269      * predicate at array location 0 returned true. Each predicate is evaluated
270      * until one returns true. If no predicates evaluate to true, the default
271      * transformer is called. If the default transformer is null, null is returned.
272      * 
273      * @see org.apache.commons.collections.functors.SwitchTransformer
274      * 
275      * @param predicates  an array of predicates to check
276      * @param transformers  an array of transformers to call
277      * @param defaultTransformer  the default to call if no predicate matches, null means return null
278      * @return the transformer
279      * @throws IllegalArgumentException if the either array is null
280      * @throws IllegalArgumentException if the either array has 0 elements
281      * @throws IllegalArgumentException if any element in the arrays is null
282      * @throws IllegalArgumentException if the arrays are different sizes
283      */
284     public static Transformer switchTransformer(Predicate[] predicates, Transformer[] transformers, Transformer defaultTransformer) {
285         return SwitchTransformer.getInstance(predicates, transformers, defaultTransformer);
286     }
287 
288     /**
289      * Create a new Transformer that calls one of the transformers depending 
290      * on the predicates. 
291      * <p>
292      * The Map consists of Predicate keys and Transformer values. A transformer 
293      * is called if its matching predicate returns true. Each predicate is evaluated
294      * until one returns true. If no predicates evaluate to true, the default
295      * transformer is called. The default transformer is set in the map with a 
296      * null key. If no default transformer is set, null will be returned in a default
297      * case. The ordering is that of the iterator() method on the entryset collection 
298      * of the map.
299      * 
300      * @see org.apache.commons.collections.functors.SwitchTransformer
301      * 
302      * @param predicatesAndTransformers  a map of predicates to transformers
303      * @return the transformer
304      * @throws IllegalArgumentException if the map is null
305      * @throws IllegalArgumentException if the map is empty
306      * @throws IllegalArgumentException if any transformer in the map is null
307      * @throws ClassCastException  if the map elements are of the wrong type
308      */
309     public static Transformer switchTransformer(Map   predicatesAndTransformers) {
310         return SwitchTransformer.getInstance(predicatesAndTransformers);
311     }
312 
313     /**
314      * Create a new Transformer that uses the input object as a key to find the
315      * transformer to call. 
316      * <p>
317      * The Map consists of object keys and Transformer values. A transformer 
318      * is called if the input object equals the key. If there is no match, the
319      * default transformer is called. The default transformer is set in the map
320      * using a null key. If no default is set, null will be returned in a default case.
321      * 
322      * @see org.apache.commons.collections.functors.SwitchTransformer
323      * 
324      * @param objectsAndTransformers  a map of objects to transformers
325      * @return the transformer
326      * @throws IllegalArgumentException if the map is null
327      * @throws IllegalArgumentException if the map is empty
328      * @throws IllegalArgumentException if any transformer in the map is null
329      */
330     public static Transformer switchMapTransformer(Map   objectsAndTransformers) {
331         Transformer[] trs = null;
332         Predicate[] preds = null;
333         if (objectsAndTransformers == null) {
334             throw new IllegalArgumentException  ("The object and transformer map must not be null");
335         }
336         Transformer def = (Transformer) objectsAndTransformers.remove(null);
337         int size = objectsAndTransformers.size();
338         trs = new Transformer[size];
339         preds = new Predicate[size];
340         int i = 0;
341         for (Iterator   it = objectsAndTransformers.entrySet().iterator(); it.hasNext();) {
342             Map.Entry   entry = (Map.Entry  ) it.next();
343             preds[i] = EqualPredicate.getInstance(entry.getKey());
344             trs[i] = (Transformer) entry.getValue();
345             i++;
346         }
347         return switchTransformer(preds, trs, def);
348     }
349 
350     /**
351      * Gets a Transformer that expects an input Class object that it will instantiate.
352      * 
353      * @see org.apache.commons.collections.functors.InstantiateTransformer
354      * 
355      * @return the transformer
356      */
357     public static Transformer instantiateTransformer() {
358         return InstantiateTransformer.NO_ARG_INSTANCE;
359     }
360 
361     /** 
362      * Creates a Transformer that expects an input Class object that it will 
363      * instantiate. The constructor used is determined by the arguments specified
364      * to this method.
365      *
366      * @see org.apache.commons.collections.functors.InstantiateTransformer
367      * 
368      * @param paramTypes  parameter types for the constructor, can be null
369      * @param args  the arguments to pass to the constructor, can be null
370      * @return the transformer
371      * @throws IllegalArgumentException if the paramTypes and args don't match
372      */
373     public static Transformer instantiateTransformer(Class  [] paramTypes, Object  [] args) {
374         return InstantiateTransformer.getInstance(paramTypes, args);
375     }
376 
377     /** 
378      * Creates a Transformer that uses the passed in Map to transform the input 
379      * object (as a simple lookup).
380      *
381      * @see org.apache.commons.collections.functors.MapTransformer
382      * 
383      * @param map  the map to use to transform the objects
384      * @return the transformer
385      * @throws IllegalArgumentException if the map is null
386      */
387     public static Transformer mapTransformer(Map   map) {
388         return MapTransformer.getInstance(map);
389     }
390 
391     /**
392      * Gets a Transformer that invokes a method on the input object.
393      * The method must have no parameters. If the input object is null, 
394      * null is returned.
395      * <p>
396      * For example, <code>TransformerUtils.invokerTransformer("getName");</code>
397      * will call the <code>getName/code> method on the input object to 
398      * determine the transformer result.
399      * 
400      * @see org.apache.commons.collections.functors.InvokerTransformer
401      * 
402      * @param methodName  the method name to call on the input object, may not be null
403      * @return the transformer
404      * @throws IllegalArgumentException if the methodName is null.
405      */
406     public static Transformer invokerTransformer(String   methodName){
407         return InvokerTransformer.getInstance(methodName, null, null);
408     }
409 
410     /**
411      * Gets a Transformer that invokes a method on the input object.
412      * The method parameters are specified. If the input object is null, 
413      * null is returned.
414      * 
415      * @see org.apache.commons.collections.functors.InvokerTransformer
416      * 
417      * @param methodName  the name of the method
418      * @param paramTypes  the parameter types
419      * @param args  the arguments
420      * @return the transformer
421      * @throws IllegalArgumentException if the method name is null
422      * @throws IllegalArgumentException if the paramTypes and args don't match
423      */
424     public static Transformer invokerTransformer(String   methodName, Class  [] paramTypes, Object  [] args){
425         return InvokerTransformer.getInstance(methodName, paramTypes, args);
426     }
427 
428     /**
429      * Gets a transformer that returns a <code>java.lang.String</code>
430      * representation of the input object. This is achieved via the
431      * <code>toString</code> method, <code>null</code> returns 'null'.
432      * 
433      * @see org.apache.commons.collections.functors.StringValueTransformer
434      * 
435      * @return the transformer
436      */
437     public static Transformer stringValueTransformer() {
438         return StringValueTransformer.INSTANCE;
439     }
440     
441 }
442
A to Z: JavaDoc & Examples Daily Java News & Articles Open Source Projects Open Source Codes Free Computer Books Remove Frame
Popular Tags