001: /*
002: * Copyright 2002-2004 The Apache Software Foundation
003: *
004: * Licensed under the Apache License, Version 2.0 (the "License");
005: * you may not use this file except in compliance with the License.
006: * You may obtain a copy of the License at
007: *
008: * http://www.apache.org/licenses/LICENSE-2.0
009: *
010: * Unless required by applicable law or agreed to in writing, software
011: * distributed under the License is distributed on an "AS IS" BASIS,
012: * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013: * See the License for the specific language governing permissions and
014: * limitations under the License.
015: */
016: package org.apache.commons.collections;
017:
018: import java.util.Collection;
019: import java.util.Iterator;
020: import java.util.Map;
021:
022: import org.apache.commons.collections.functors.ChainedTransformer;
023: import org.apache.commons.collections.functors.CloneTransformer;
024: import org.apache.commons.collections.functors.ClosureTransformer;
025: import org.apache.commons.collections.functors.ConstantTransformer;
026: import org.apache.commons.collections.functors.EqualPredicate;
027: import org.apache.commons.collections.functors.ExceptionTransformer;
028: import org.apache.commons.collections.functors.FactoryTransformer;
029: import org.apache.commons.collections.functors.InstantiateTransformer;
030: import org.apache.commons.collections.functors.InvokerTransformer;
031: import org.apache.commons.collections.functors.MapTransformer;
032: import org.apache.commons.collections.functors.NOPTransformer;
033: import org.apache.commons.collections.functors.PredicateTransformer;
034: import org.apache.commons.collections.functors.StringValueTransformer;
035: import org.apache.commons.collections.functors.SwitchTransformer;
036:
037: /**
038: * <code>TransformerUtils</code> provides reference implementations and
039: * utilities for the Transformer functor interface. The supplied transformers are:
040: * <ul>
041: * <li>Invoker - returns the result of a method call on the input object
042: * <li>Clone - returns a clone of the input object
043: * <li>Constant - always returns the same object
044: * <li>Closure - performs a Closure and returns the input object
045: * <li>Predicate - returns the result of the predicate as a Boolean
046: * <li>Factory - returns a new object from a factory
047: * <li>Chained - chains two or more transformers together
048: * <li>Switch - calls one transformer based on one or more predicates
049: * <li>SwitchMap - calls one transformer looked up from a Map
050: * <li>Instantiate - the Class input object is instantiated
051: * <li>Map - returns an object from a supplied Map
052: * <li>Null - always returns null
053: * <li>NOP - returns the input object, which should be immutable
054: * <li>Exception - always throws an exception
055: * <li>StringValue - returns a <code>java.lang.String</code> representation of the input object
056: * </ul>
057: * All the supplied transformers are Serializable.
058: *
059: * @since Commons Collections 3.0
060: * @version $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
061: *
062: * @author Stephen Colebourne
063: * @author James Carman
064: */
065: public class TransformerUtils {
066:
067: /**
068: * This class is not normally instantiated.
069: */
070: public TransformerUtils() {
071: super ();
072: }
073:
074: /**
075: * Gets a transformer that always throws an exception.
076: * This could be useful during testing as a placeholder.
077: *
078: * @see org.apache.commons.collections.functors.ExceptionTransformer
079: *
080: * @return the transformer
081: */
082: public static Transformer exceptionTransformer() {
083: return ExceptionTransformer.INSTANCE;
084: }
085:
086: /**
087: * Gets a transformer that always returns null.
088: *
089: * @see org.apache.commons.collections.functors.ConstantTransformer
090: *
091: * @return the transformer
092: */
093: public static Transformer nullTransformer() {
094: return ConstantTransformer.NULL_INSTANCE;
095: }
096:
097: /**
098: * Gets a transformer that returns the input object.
099: * 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(
138: 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(
196: Transformer transformer1, Transformer transformer2) {
197: return ChainedTransformer.getInstance(transformer1,
198: transformer2);
199: }
200:
201: /**
202: * Create a new Transformer that calls each transformer in turn, passing the
203: * result into the next transformer.
204: *
205: * @see org.apache.commons.collections.functors.ChainedTransformer
206: *
207: * @param transformers an array of transformers to chain
208: * @return the transformer
209: * @throws IllegalArgumentException if the transformers array is null
210: * @throws IllegalArgumentException if any transformer in the array is null
211: */
212: public static Transformer chainedTransformer(
213: Transformer[] transformers) {
214: return ChainedTransformer.getInstance(transformers);
215: }
216:
217: /**
218: * Create a new Transformer that calls each transformer in turn, passing the
219: * result into the next transformer. The ordering is that of the iterator()
220: * method on the collection.
221: *
222: * @see org.apache.commons.collections.functors.ChainedTransformer
223: *
224: * @param transformers a collection of transformers to chain
225: * @return the transformer
226: * @throws IllegalArgumentException if the transformers collection is null
227: * @throws IllegalArgumentException if any transformer in the collection is null
228: */
229: public static Transformer chainedTransformer(Collection transformers) {
230: return ChainedTransformer.getInstance(transformers);
231: }
232:
233: /**
234: * Create a new Transformer that calls one of two transformers depending
235: * on the specified predicate.
236: *
237: * @see org.apache.commons.collections.functors.SwitchTransformer
238: *
239: * @param predicate the predicate to switch on
240: * @param trueTransformer the transformer called if the predicate is true
241: * @param falseTransformer the transformer called if the predicate is false
242: * @return the transformer
243: * @throws IllegalArgumentException if the predicate is null
244: * @throws IllegalArgumentException if either transformer is null
245: */
246: public static Transformer switchTransformer(Predicate predicate,
247: Transformer trueTransformer, Transformer falseTransformer) {
248: return SwitchTransformer
249: .getInstance(new Predicate[] { predicate },
250: new Transformer[] { trueTransformer },
251: falseTransformer);
252: }
253:
254: /**
255: * Create a new Transformer that calls one of the transformers depending
256: * on the predicates. The transformer at array location 0 is called if the
257: * predicate at array location 0 returned true. Each predicate is evaluated
258: * until one returns true. If no predicates evaluate to true, null is returned.
259: *
260: * @see org.apache.commons.collections.functors.SwitchTransformer
261: *
262: * @param predicates an array of predicates to check
263: * @param transformers an array of transformers to call
264: * @return the transformer
265: * @throws IllegalArgumentException if the either array is null
266: * @throws IllegalArgumentException if the either array has 0 elements
267: * @throws IllegalArgumentException if any element in the arrays is null
268: * @throws IllegalArgumentException if the arrays are different sizes
269: */
270: public static Transformer switchTransformer(Predicate[] predicates,
271: Transformer[] transformers) {
272: return SwitchTransformer.getInstance(predicates, transformers,
273: null);
274: }
275:
276: /**
277: * Create a new Transformer that calls one of the transformers depending
278: * on the predicates. The transformer at array location 0 is called if the
279: * predicate at array location 0 returned true. Each predicate is evaluated
280: * until one returns true. If no predicates evaluate to true, the default
281: * transformer is called. If the default transformer is null, null is returned.
282: *
283: * @see org.apache.commons.collections.functors.SwitchTransformer
284: *
285: * @param predicates an array of predicates to check
286: * @param transformers an array of transformers to call
287: * @param defaultTransformer the default to call if no predicate matches, null means return null
288: * @return the transformer
289: * @throws IllegalArgumentException if the either array is null
290: * @throws IllegalArgumentException if the either array has 0 elements
291: * @throws IllegalArgumentException if any element in the arrays is null
292: * @throws IllegalArgumentException if the arrays are different sizes
293: */
294: public static Transformer switchTransformer(Predicate[] predicates,
295: Transformer[] transformers, Transformer defaultTransformer) {
296: return SwitchTransformer.getInstance(predicates, transformers,
297: defaultTransformer);
298: }
299:
300: /**
301: * Create a new Transformer that calls one of the transformers depending
302: * on the predicates.
303: * <p>
304: * The Map consists of Predicate keys and Transformer values. A transformer
305: * is called if its matching predicate returns true. Each predicate is evaluated
306: * until one returns true. If no predicates evaluate to true, the default
307: * transformer is called. The default transformer is set in the map with a
308: * null key. If no default transformer is set, null will be returned in a default
309: * case. The ordering is that of the iterator() method on the entryset collection
310: * of the map.
311: *
312: * @see org.apache.commons.collections.functors.SwitchTransformer
313: *
314: * @param predicatesAndTransformers a map of predicates to transformers
315: * @return the transformer
316: * @throws IllegalArgumentException if the map is null
317: * @throws IllegalArgumentException if the map is empty
318: * @throws IllegalArgumentException if any transformer in the map is null
319: * @throws ClassCastException if the map elements are of the wrong type
320: */
321: public static Transformer switchTransformer(
322: Map predicatesAndTransformers) {
323: return SwitchTransformer.getInstance(predicatesAndTransformers);
324: }
325:
326: /**
327: * Create a new Transformer that uses the input object as a key to find the
328: * transformer to call.
329: * <p>
330: * The Map consists of object keys and Transformer values. A transformer
331: * is called if the input object equals the key. If there is no match, the
332: * default transformer is called. The default transformer is set in the map
333: * using a null key. If no default is set, null will be returned in a default case.
334: *
335: * @see org.apache.commons.collections.functors.SwitchTransformer
336: *
337: * @param objectsAndTransformers a map of objects to transformers
338: * @return the transformer
339: * @throws IllegalArgumentException if the map is null
340: * @throws IllegalArgumentException if the map is empty
341: * @throws IllegalArgumentException if any transformer in the map is null
342: */
343: public static Transformer switchMapTransformer(
344: Map objectsAndTransformers) {
345: Transformer[] trs = null;
346: Predicate[] preds = null;
347: if (objectsAndTransformers == null) {
348: throw new IllegalArgumentException(
349: "The object and transformer map must not be null");
350: }
351: Transformer def = (Transformer) objectsAndTransformers
352: .remove(null);
353: int size = objectsAndTransformers.size();
354: trs = new Transformer[size];
355: preds = new Predicate[size];
356: int i = 0;
357: for (Iterator it = objectsAndTransformers.entrySet().iterator(); it
358: .hasNext();) {
359: Map.Entry entry = (Map.Entry) it.next();
360: preds[i] = EqualPredicate.getInstance(entry.getKey());
361: trs[i] = (Transformer) entry.getValue();
362: i++;
363: }
364: return switchTransformer(preds, trs, def);
365: }
366:
367: /**
368: * Gets a Transformer that expects an input Class object that it will instantiate.
369: *
370: * @see org.apache.commons.collections.functors.InstantiateTransformer
371: *
372: * @return the transformer
373: */
374: public static Transformer instantiateTransformer() {
375: return InstantiateTransformer.NO_ARG_INSTANCE;
376: }
377:
378: /**
379: * Creates a Transformer that expects an input Class object that it will
380: * instantiate. The constructor used is determined by the arguments specified
381: * to this method.
382: *
383: * @see org.apache.commons.collections.functors.InstantiateTransformer
384: *
385: * @param paramTypes parameter types for the constructor, can be null
386: * @param args the arguments to pass to the constructor, can be null
387: * @return the transformer
388: * @throws IllegalArgumentException if the paramTypes and args don't match
389: */
390: public static Transformer instantiateTransformer(
391: Class[] paramTypes, Object[] args) {
392: return InstantiateTransformer.getInstance(paramTypes, args);
393: }
394:
395: /**
396: * Creates a Transformer that uses the passed in Map to transform the input
397: * object (as a simple lookup).
398: *
399: * @see org.apache.commons.collections.functors.MapTransformer
400: *
401: * @param map the map to use to transform the objects
402: * @return the transformer
403: * @throws IllegalArgumentException if the map is null
404: */
405: public static Transformer mapTransformer(Map map) {
406: return MapTransformer.getInstance(map);
407: }
408:
409: /**
410: * Gets a Transformer that invokes a method on the input object.
411: * The method must have no parameters. If the input object is null,
412: * null is returned.
413: * <p>
414: * For example, <code>TransformerUtils.invokerTransformer("getName");</code>
415: * will call the <code>getName/code> method on the input object to
416: * determine the transformer result.
417: *
418: * @see org.apache.commons.collections.functors.InvokerTransformer
419: *
420: * @param methodName the method name to call on the input object, may not be null
421: * @return the transformer
422: * @throws IllegalArgumentException if the methodName is null.
423: */
424: public static Transformer invokerTransformer(String methodName) {
425: return InvokerTransformer.getInstance(methodName, null, null);
426: }
427:
428: /**
429: * Gets a Transformer that invokes a method on the input object.
430: * The method parameters are specified. If the input object is null,
431: * null is returned.
432: *
433: * @see org.apache.commons.collections.functors.InvokerTransformer
434: *
435: * @param methodName the name of the method
436: * @param paramTypes the parameter types
437: * @param args the arguments
438: * @return the transformer
439: * @throws IllegalArgumentException if the method name is null
440: * @throws IllegalArgumentException if the paramTypes and args don't match
441: */
442: public static Transformer invokerTransformer(String methodName,
443: Class[] paramTypes, Object[] args) {
444: return InvokerTransformer.getInstance(methodName, paramTypes,
445: args);
446: }
447:
448: /**
449: * Gets a transformer that returns a <code>java.lang.String</code>
450: * representation of the input object. This is achieved via the
451: * <code>toString</code> method, <code>null</code> returns 'null'.
452: *
453: * @see org.apache.commons.collections.functors.StringValueTransformer
454: *
455: * @return the transformer
456: */
457: public static Transformer stringValueTransformer() {
458: return StringValueTransformer.INSTANCE;
459: }
460:
461: }
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