1 package org.codehaus.plexus.util.introspection;
2
3 /*
4 * Copyright The Codehaus Foundation.
5 *
6 * Licensed under the Apache License, Version 2.0 (the "License");
7 * you may not use this file except in compliance with the License.
8 * You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18
19 import java.lang.reflect.Method;
20 import java.util.ArrayList;
21 import java.util.Hashtable;
22 import java.util.Iterator;
23 import java.util.LinkedList;
24 import java.util.List;
25 import java.util.Map;
26
27 /**
28 * @author <a href="mailto:jvanzyl@apache.org">Jason van Zyl</a>
29 * @author <a href="mailto:bob@werken.com">Bob McWhirter</a>
30 * @author <a href="mailto:Christoph.Reck@dlr.de">Christoph Reck</a>
31 * @author <a href="mailto:geirm@optonline.net">Geir Magnusson Jr.</a>
32 * @author <a href="mailto:szegedia@freemail.hu">Attila Szegedi</a>
33 *
34 */
35 public class MethodMap
36 {
37 private static final int MORE_SPECIFIC = 0;
38
39 private static final int LESS_SPECIFIC = 1;
40
41 private static final int INCOMPARABLE = 2;
42
43 /**
44 * Keep track of all methods with the same name.
45 */
46 Map<String, List<Method>> methodByNameMap = new Hashtable<String, List<Method>>();
47
48 /**
49 * Add a method to a list of methods by name. For a particular class we are keeping track of all the methods with
50 * the same name.
51 *
52 * @param method The method
53 */
54 public void add( Method method )
55 {
56 String methodName = method.getName();
57
58 List<Method> l = get( methodName );
59
60 if ( l == null )
61 {
62 l = new ArrayList<Method>();
63 methodByNameMap.put( methodName, l );
64 }
65
66 l.add( method );
67 }
68
69 /**
70 * Return a list of methods with the same name.
71 *
72 * @param key The name of the method.
73 * @return List list of methods
74 */
75 public List<Method> get( String key )
76 {
77 return methodByNameMap.get( key );
78 }
79
80 /**
81 * <p>
82 * Find a method. Attempts to find the most specific applicable method using the algorithm described in the JLS
83 * section 15.12.2 (with the exception that it can't distinguish a primitive type argument from an object type
84 * argument, since in reflection primitive type arguments are represented by their object counterparts, so for an
85 * argument of type (say) java.lang.Integer, it will not be able to decide between a method that takes int and a
86 * method that takes java.lang.Integer as a parameter.
87 * </p>
88 * <p>
89 * This turns out to be a relatively rare case where this is needed - however, functionality like this is needed.
90 * </p>
91 *
92 * @param methodName name of method
93 * @param args the actual arguments with which the method is called
94 * @return the most specific applicable method, or null if no method is applicable.
95 * @throws AmbiguousException if there is more than one maximally specific applicable method
96 */
97 public Method find( String methodName, Object[] args )
98 throws AmbiguousException
99 {
100 List<Method> methodList = get( methodName );
101
102 if ( methodList == null )
103 {
104 return null;
105 }
106
107 int l = args.length;
108 Class[] classes = new Class[l];
109
110 for ( int i = 0; i < l; ++i )
111 {
112 Object arg = args[i];
113
114 /*
115 * if we are careful down below, a null argument goes in there so we can know that the null was passed to
116 * the method
117 */
118 classes[i] = arg == null ? null : arg.getClass();
119 }
120
121 return getMostSpecific( methodList, classes );
122 }
123
124 /**
125 * simple distinguishable exception, used when we run across ambiguous overloading
126 */
127 public static class AmbiguousException
128 extends Exception
129 {
130 }
131
132 private static Method getMostSpecific( List<Method> methods, Class[] classes )
133 throws AmbiguousException
134 {
135 LinkedList<Method> applicables = getApplicables( methods, classes );
136
137 if ( applicables.isEmpty() )
138 {
139 return null;
140 }
141
142 if ( applicables.size() == 1 )
143 {
144 return applicables.getFirst();
145 }
146
147 /*
148 * This list will contain the maximally specific methods. Hopefully at the end of the below loop, the list will
149 * contain exactly one method, (the most specific method) otherwise we have ambiguity.
150 */
151
152 LinkedList<Method> maximals = new LinkedList<Method>();
153
154 for ( Method app : applicables )
155 {
156 Class[] appArgs = app.getParameterTypes();
157 boolean lessSpecific = false;
158
159 for ( Iterator<Method> maximal = maximals.iterator(); !lessSpecific && maximal.hasNext(); )
160 {
161 Method max = maximal.next();
162
163 switch ( moreSpecific( appArgs, max.getParameterTypes() ) )
164 {
165 case MORE_SPECIFIC:
166 {
167 /*
168 * This method is more specific than the previously known maximally specific, so remove the old
169 * maximum.
170 */
171
172 maximal.remove();
173 break;
174 }
175
176 case LESS_SPECIFIC:
177 {
178 /*
179 * This method is less specific than some of the currently known maximally specific methods, so
180 * we won't add it into the set of maximally specific methods
181 */
182
183 lessSpecific = true;
184 break;
185 }
186 }
187 }
188
189 if ( !lessSpecific )
190 {
191 maximals.addLast( app );
192 }
193 }
194
195 if ( maximals.size() > 1 )
196 {
197 // We have more than one maximally specific method
198 throw new AmbiguousException();
199 }
200
201 return maximals.getFirst();
202 }
203
204 /**
205 * Determines which method signature (represented by a class array) is more specific. This defines a partial
206 * ordering on the method signatures.
207 *
208 * @param c1 first signature to compare
209 * @param c2 second signature to compare
210 * @return MORE_SPECIFIC if c1 is more specific than c2, LESS_SPECIFIC if c1 is less specific than c2, INCOMPARABLE
211 * if they are incomparable.
212 */
213 private static int moreSpecific( Class[] c1, Class[] c2 )
214 {
215 boolean c1MoreSpecific = false;
216 boolean c2MoreSpecific = false;
217
218 for ( int i = 0; i < c1.length; ++i )
219 {
220 if ( c1[i] != c2[i] )
221 {
222 c1MoreSpecific = c1MoreSpecific || isStrictMethodInvocationConvertible( c2[i], c1[i] );
223 c2MoreSpecific = c2MoreSpecific || isStrictMethodInvocationConvertible( c1[i], c2[i] );
224 }
225 }
226
227 if ( c1MoreSpecific )
228 {
229 if ( c2MoreSpecific )
230 {
231 /*
232 * Incomparable due to cross-assignable arguments (i.e. foo(String, Object) vs. foo(Object, String))
233 */
234
235 return INCOMPARABLE;
236 }
237
238 return MORE_SPECIFIC;
239 }
240
241 if ( c2MoreSpecific )
242 {
243 return LESS_SPECIFIC;
244 }
245
246 /*
247 * Incomparable due to non-related arguments (i.e. foo(Runnable) vs. foo(Serializable))
248 */
249
250 return INCOMPARABLE;
251 }
252
253 /**
254 * Returns all methods that are applicable to actual argument types.
255 *
256 * @param methods list of all candidate methods
257 * @param classes the actual types of the arguments
258 * @return a list that contains only applicable methods (number of formal and actual arguments matches, and argument
259 * types are assignable to formal types through a method invocation conversion).
260 */
261 private static LinkedList<Method> getApplicables( List<Method> methods, Class[] classes )
262 {
263 LinkedList<Method> list = new LinkedList<Method>();
264
265 for ( Object method1 : methods )
266 {
267 Method method = (Method) method1;
268
269 if ( isApplicable( method, classes ) )
270 {
271 list.add( method );
272 }
273
274 }
275 return list;
276 }
277
278 /**
279 * Returns true if the supplied method is applicable to actual argument types.
280 *
281 * @param method The method to check for applicability
282 * @param classes The arguments
283 * @return true if the method applies to the parameter types
284 */
285 private static boolean isApplicable( Method method, Class[] classes )
286 {
287 Class[] methodArgs = method.getParameterTypes();
288
289 if ( methodArgs.length != classes.length )
290 {
291 return false;
292 }
293
294 for ( int i = 0; i < classes.length; ++i )
295 {
296 if ( !isMethodInvocationConvertible( methodArgs[i], classes[i] ) )
297 {
298 return false;
299 }
300 }
301
302 return true;
303 }
304
305 /**
306 * Determines whether a type represented by a class object is convertible to another type represented by a class
307 * object using a method invocation conversion, treating object types of primitive types as if they were primitive
308 * types (that is, a Boolean actual parameter type matches boolean primitive formal type). This behavior is because
309 * this method is used to determine applicable methods for an actual parameter list, and primitive types are
310 * represented by their object duals in reflective method calls.
311 *
312 * @param formal the formal parameter type to which the actual parameter type should be convertible
313 * @param actual the actual parameter type.
314 * @return true if either formal type is assignable from actual type, or formal is a primitive type and actual is
315 * its corresponding object type or an object type of a primitive type that can be converted to the formal
316 * type.
317 */
318 private static boolean isMethodInvocationConvertible( Class formal, Class actual )
319 {
320 /*
321 * if it's a null, it means the arg was null
322 */
323 if ( actual == null && !formal.isPrimitive() )
324 {
325 return true;
326 }
327
328 /*
329 * Check for identity or widening reference conversion
330 */
331
332 if ( actual != null && formal.isAssignableFrom( actual ) )
333 {
334 return true;
335 }
336
337 /*
338 * Check for boxing with widening primitive conversion. Note that actual parameters are never primitives.
339 */
340
341 if ( formal.isPrimitive() )
342 {
343 if ( formal == Boolean.TYPE && actual == Boolean.class )
344 return true;
345 if ( formal == Character.TYPE && actual == Character.class )
346 return true;
347 if ( formal == Byte.TYPE && actual == Byte.class )
348 return true;
349 if ( formal == Short.TYPE && ( actual == Short.class || actual == Byte.class ) )
350 return true;
351 if ( formal == Integer.TYPE
352 && ( actual == Integer.class || actual == Short.class || actual == Byte.class ) )
353 return true;
354 if ( formal == Long.TYPE && ( actual == Long.class || actual == Integer.class || actual == Short.class
355 || actual == Byte.class ) )
356 return true;
357 if ( formal == Float.TYPE && ( actual == Float.class || actual == Long.class || actual == Integer.class
358 || actual == Short.class || actual == Byte.class ) )
359 return true;
360 if ( formal == Double.TYPE && ( actual == Double.class || actual == Float.class || actual == Long.class
361 || actual == Integer.class || actual == Short.class || actual == Byte.class ) )
362 return true;
363 }
364
365 return false;
366 }
367
368 /**
369 * Determines whether a type represented by a class object is convertible to another type represented by a class
370 * object using a method invocation conversion, without matching object and primitive types. This method is used to
371 * determine the more specific type when comparing signatures of methods.
372 *
373 * @param formal the formal parameter type to which the actual parameter type should be convertible
374 * @param actual the actual parameter type.
375 * @return true if either formal type is assignable from actual type, or formal and actual are both primitive types
376 * and actual can be subject to widening conversion to formal.
377 */
378 private static boolean isStrictMethodInvocationConvertible( Class formal, Class actual )
379 {
380 /*
381 * we shouldn't get a null into, but if so
382 */
383 if ( actual == null && !formal.isPrimitive() )
384 {
385 return true;
386 }
387
388 /*
389 * Check for identity or widening reference conversion
390 */
391
392 if ( formal.isAssignableFrom( actual ) )
393 {
394 return true;
395 }
396
397 /*
398 * Check for widening primitive conversion.
399 */
400
401 if ( formal.isPrimitive() )
402 {
403 if ( formal == Short.TYPE && ( actual == Byte.TYPE ) )
404 return true;
405 if ( formal == Integer.TYPE && ( actual == Short.TYPE || actual == Byte.TYPE ) )
406 return true;
407 if ( formal == Long.TYPE && ( actual == Integer.TYPE || actual == Short.TYPE || actual == Byte.TYPE ) )
408 return true;
409 if ( formal == Float.TYPE
410 && ( actual == Long.TYPE || actual == Integer.TYPE || actual == Short.TYPE || actual == Byte.TYPE ) )
411 return true;
412 if ( formal == Double.TYPE && ( actual == Float.TYPE || actual == Long.TYPE || actual == Integer.TYPE
413 || actual == Short.TYPE || actual == Byte.TYPE ) )
414 return true;
415 }
416 return false;
417 }
418 }