ClosureUtils


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.ChainedClosure;
23  import org.apache.commons.collections.functors.EqualPredicate;
24  import org.apache.commons.collections.functors.ExceptionClosure;
25  import org.apache.commons.collections.functors.ForClosure;
26  import org.apache.commons.collections.functors.IfClosure;
27  import org.apache.commons.collections.functors.InvokerTransformer;
28  import org.apache.commons.collections.functors.NOPClosure;
29  import org.apache.commons.collections.functors.SwitchClosure;
30  import org.apache.commons.collections.functors.TransformerClosure;
31  import org.apache.commons.collections.functors.WhileClosure;
32  
33  /**
34   * <code>ClosureUtils</code> provides reference implementations and utilities
35   * for the Closure functor interface. The supplied closures are:
36   * <ul>
37   * <li>Invoker - invokes a method on the input object
38   * <li>For - repeatedly calls a closure for a fixed number of times
39   * <li>While - repeatedly calls a closure while a predicate is true
40   * <li>DoWhile - repeatedly calls a closure while a predicate is true
41   * <li>Chained - chains two or more closures together
42   * <li>Switch - calls one closure based on one or more predicates
43   * <li>SwitchMap - calls one closure looked up from a Map
44   * <li>Transformer - wraps a Transformer as a Closure
45   * <li>NOP - does nothing
46   * <li>Exception - always throws an exception
47   * </ul>
48   * All the supplied closures are Serializable.
49   * 
50   * @since Commons Collections 3.0
51   * @version $Revision: 1.9 $ $Date: 2004/05/26 21:50:52 $
52   *
53   * @author Stephen Colebourne
54   */
55  public class ClosureUtils {
56  
57      /**
58       * This class is not normally instantiated.
59       */
60      public ClosureUtils() {
61          super();
62      }
63  
64      /**
65       * Gets a Closure that always throws an exception.
66       * This could be useful during testing as a placeholder.
67       *
68       * @see org.apache.commons.collections.functors.ExceptionClosure
69       * 
70       * @return the closure
71       */
72      public static Closure exceptionClosure() {
73          return ExceptionClosure.INSTANCE;
74      }
75  
76      /**
77       * Gets a Closure that will do nothing.
78       * This could be useful during testing as a placeholder.
79       *
80       * @see org.apache.commons.collections.functors.NOPClosure
81       * 
82       * @return the closure
83       */
84      public static Closure nopClosure() {
85          return NOPClosure.INSTANCE;
86      }
87  
88      /**
89       * Creates a Closure that calls a Transformer each time it is called.
90       * The transformer will be called using the closure's input object.
91       * The transformer's result will be ignored.
92       *
93       * @see org.apache.commons.collections.functors.TransformerClosure
94       * 
95       * @param transformer  the transformer to run each time in the closure, null means nop
96       * @return the closure
97       */
98      public static Closure asClosure(Transformer transformer) {
99          return TransformerClosure.getInstance(transformer);
100     }
101 
102     /**
103      * Creates a Closure that will call the closure <code>count</code> times.
104      * <p>
105      * A null closure or zero count returns the <code>NOPClosure</code>.
106      *
107      * @see org.apache.commons.collections.functors.ForClosure
108      * 
109      * @param count  the number of times to loop
110      * @param closure  the closure to call repeatedly
111      * @return the <code>for</code> closure
112      */
113     public static Closure forClosure(int count, Closure closure) {
114         return ForClosure.getInstance(count, closure);
115     }
116 
117     /**
118      * Creates a Closure that will call the closure repeatedly until the 
119      * predicate returns false.
120      *
121      * @see org.apache.commons.collections.functors.WhileClosure
122      * 
123      * @param predicate  the predicate to use as an end of loop test, not null
124      * @param closure  the closure to call repeatedly, not null
125      * @return the <code>while</code> closure
126      * @throws IllegalArgumentException if either argument is null
127      */
128     public static Closure whileClosure(Predicate predicate, Closure closure) {
129         return WhileClosure.getInstance(predicate, closure, false);
130     }
131 
132     /**
133      * Creates a Closure that will call the closure once and then repeatedly
134      * until the predicate returns false.
135      *
136      * @see org.apache.commons.collections.functors.WhileClosure
137      * 
138      * @param closure  the closure to call repeatedly, not null
139      * @param predicate  the predicate to use as an end of loop test, not null
140      * @return the <code>do-while</code> closure
141      * @throws IllegalArgumentException if either argument is null
142      */
143     public static Closure doWhileClosure(Closure closure, Predicate predicate) {
144         return WhileClosure.getInstance(predicate, closure, true);
145     }
146 
147     /**
148      * Creates a Closure that will invoke a specific method on the closure's
149      * input object by reflection.
150      *
151      * @see org.apache.commons.collections.functors.InvokerTransformer
152      * @see org.apache.commons.collections.functors.TransformerClosure
153      * 
154      * @param methodName  the name of the method
155      * @return the <code>invoker</code> closure
156      * @throws IllegalArgumentException if the method name is null
157      */
158     public static Closure invokerClosure(String   methodName) {
159         // reuse transformer as it has caching - this is lazy really, should have inner class here
160         return asClosure(InvokerTransformer.getInstance(methodName));
161     }
162 
163     /**
164      * Creates a Closure that will invoke a specific method on the closure's
165      * input object by reflection.
166      *
167      * @see org.apache.commons.collections.functors.InvokerTransformer
168      * @see org.apache.commons.collections.functors.TransformerClosure
169      * 
170      * @param methodName  the name of the method
171      * @param paramTypes  the parameter types
172      * @param args  the arguments
173      * @return the <code>invoker</code> closure
174      * @throws IllegalArgumentException if the method name is null
175      * @throws IllegalArgumentException if the paramTypes and args don't match
176      */
177     public static Closure invokerClosure(String   methodName, Class  [] paramTypes, Object  [] args) {
178         // reuse transformer as it has caching - this is lazy really, should have inner class here
179         return asClosure(InvokerTransformer.getInstance(methodName, paramTypes, args));
180     }
181 
182     /**
183      * Create a new Closure that calls two Closures, passing the result of
184      * the first into the second.
185      * 
186      * @see org.apache.commons.collections.functors.ChainedClosure
187      * 
188      * @param closure1  the first closure
189      * @param closure2  the second closure
190      * @return the <code>chained</code> closure
191      * @throws IllegalArgumentException if either closure is null
192      */
193     public static Closure chainedClosure(Closure closure1, Closure closure2) {
194         return ChainedClosure.getInstance(closure1, closure2);
195     }
196 
197     /**
198      * Create a new Closure that calls each closure in turn, passing the 
199      * result into the next closure.
200      * 
201      * @see org.apache.commons.collections.functors.ChainedClosure
202      * 
203      * @param closures  an array of closures to chain
204      * @return the <code>chained</code> closure
205      * @throws IllegalArgumentException if the closures array is null
206      * @throws IllegalArgumentException if any closure in the array is null
207      */
208     public static Closure chainedClosure(Closure[] closures) {
209         return ChainedClosure.getInstance(closures);
210     }
211 
212     /**
213      * Create a new Closure that calls each closure in turn, passing the 
214      * result into the next closure. The ordering is that of the iterator()
215      * method on the collection.
216      * 
217      * @see org.apache.commons.collections.functors.ChainedClosure
218      * 
219      * @param closures  a collection of closures to chain
220      * @return the <code>chained</code> closure
221      * @throws IllegalArgumentException if the closures collection is null
222      * @throws IllegalArgumentException if the closures collection is empty
223      * @throws IllegalArgumentException if any closure in the collection is null
224      */
225     public static Closure chainedClosure(Collection   closures) {
226         return ChainedClosure.getInstance(closures);
227     }
228 
229     /**
230      * Create a new Closure that calls one of two closures depending 
231      * on the specified predicate.
232      * 
233      * @see org.apache.commons.collections.functors.IfClosure
234      * 
235      * @param predicate  the predicate to switch on
236      * @param trueClosure  the closure called if the predicate is true
237      * @param falseClosure  the closure called if the predicate is false
238      * @return the <code>switch</code> closure
239      * @throws IllegalArgumentException if the predicate is null
240      * @throws IllegalArgumentException if either closure is null
241      */
242     public static Closure ifClosure(Predicate predicate, Closure trueClosure, Closure falseClosure) {
243         return IfClosure.getInstance(predicate, trueClosure, falseClosure);
244     }
245 
246     /**
247      * Create a new Closure that calls one of the closures depending 
248      * on the predicates.
249      * <p>
250      * The closure at array location 0 is called if the predicate at array 
251      * location 0 returned true. Each predicate is evaluated
252      * until one returns true.
253      * 
254      * @see org.apache.commons.collections.functors.SwitchClosure
255      * 
256      * @param predicates  an array of predicates to check, not null
257      * @param closures  an array of closures to call, not null
258      * @return the <code>switch</code> closure
259      * @throws IllegalArgumentException if the either array is null
260      * @throws IllegalArgumentException if any element in the arrays is null
261      * @throws IllegalArgumentException if the arrays are different sizes
262      */
263     public static Closure switchClosure(Predicate[] predicates, Closure[] closures) {
264         return SwitchClosure.getInstance(predicates, closures, null);
265     }
266 
267     /**
268      * Create a new Closure that calls one of the closures depending 
269      * on the predicates.
270      * <p>
271      * The closure at array location 0 is called if the predicate at array
272      * location 0 returned true. Each predicate is evaluated
273      * until one returns true. If no predicates evaluate to true, the default
274      * closure is called.
275      * 
276      * @see org.apache.commons.collections.functors.SwitchClosure
277      * 
278      * @param predicates  an array of predicates to check, not null
279      * @param closures  an array of closures to call, not null
280      * @param defaultClosure  the default to call if no predicate matches
281      * @return the <code>switch</code> closure
282      * @throws IllegalArgumentException if the either array is null
283      * @throws IllegalArgumentException if any element in the arrays is null
284      * @throws IllegalArgumentException if the arrays are different sizes
285      */
286     public static Closure switchClosure(Predicate[] predicates, Closure[] closures, Closure defaultClosure) {
287         return SwitchClosure.getInstance(predicates, closures, defaultClosure);
288     }
289     
290     /**
291      * Create a new Closure that calls one of the closures depending 
292      * on the predicates. 
293      * <p>
294      * The Map consists of Predicate keys and Closure values. A closure 
295      * is called if its matching predicate returns true. Each predicate is evaluated
296      * until one returns true. If no predicates evaluate to true, the default
297      * closure is called. The default closure is set in the map with a 
298      * null key. The ordering is that of the iterator() method on the entryset 
299      * collection of the map.
300      * 
301      * @see org.apache.commons.collections.functors.SwitchClosure
302      * 
303      * @param predicatesAndClosures  a map of predicates to closures
304      * @return the <code>switch</code> closure
305      * @throws IllegalArgumentException if the map is null
306      * @throws IllegalArgumentException if the map is empty
307      * @throws IllegalArgumentException if any closure in the map is null
308      * @throws ClassCastException  if the map elements are of the wrong type
309      */
310     public static Closure switchClosure(Map   predicatesAndClosures) {
311         return SwitchClosure.getInstance(predicatesAndClosures);
312     }
313 
314     /**
315      * Create a new Closure that uses the input object as a key to find the
316      * closure to call. 
317      * <p>
318      * The Map consists of object keys and Closure values. A closure 
319      * is called if the input object equals the key. If there is no match, the
320      * default closure is called. The default closure is set in the map
321      * using a null key.
322      * 
323      * @see org.apache.commons.collections.functors.SwitchClosure
324      * 
325      * @param objectsAndClosures  a map of objects to closures
326      * @return the closure
327      * @throws IllegalArgumentException if the map is null
328      * @throws IllegalArgumentException if the map is empty
329      * @throws IllegalArgumentException if any closure in the map is null
330      */
331     public static Closure switchMapClosure(Map   objectsAndClosures) {
332         Closure[] trs = null;
333         Predicate[] preds = null;
334         if (objectsAndClosures == null) {
335             throw new IllegalArgumentException  ("The object and closure map must not be null");
336         }
337         Closure def = (Closure) objectsAndClosures.remove(null);
338         int size = objectsAndClosures.size();
339         trs = new Closure[size];
340         preds = new Predicate[size];
341         int i = 0;
342         for (Iterator   it = objectsAndClosures.entrySet().iterator(); it.hasNext();) {
343             Map.Entry   entry = (Map.Entry  ) it.next();
344             preds[i] = EqualPredicate.getInstance(entry.getKey());
345             trs[i] = (Closure) entry.getValue();
346             i++;
347         }
348         return switchClosure(preds, trs, def);
349     }
350 
351 }
352
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