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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   * @version $Id$
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 }