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1   /*
2    * Copyright 2001,2004 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  
17  package org.apache.commons.jexl.util.introspection;
18  
19  
20  import java.util.Map;
21  import java.util.Set;
22  import java.util.HashMap;
23  import java.util.HashSet;
24  
25  import java.lang.reflect.Method;
26  
27  /***
28   * This basic function of this class is to return a Method
29   * object for a particular class given the name of a method
30   * and the parameters to the method in the form of an Object[]
31   *
32   * The first time the Introspector sees a 
33   * class it creates a class method map for the
34   * class in question. Basically the class method map
35   * is a Hastable where Method objects are keyed by a
36   * concatenation of the method name and the names of
37   * classes that make up the parameters.
38   *
39   * For example, a method with the following signature:
40   *
41   * public void method(String a, StringBuffer b)
42   *
43   * would be mapped by the key:
44   *
45   * "method" + "java.lang.String" + "java.lang.StringBuffer"
46   *
47   * This mapping is performed for all the methods in a class
48   * and stored for 
49   * @author <a href="mailto:jvanzyl@apache.org">Jason van Zyl</a>
50   * @author <a href="mailto:bob@werken.com">Bob McWhirter</a>
51   * @author <a href="mailto:szegedia@freemail.hu">Attila Szegedi</a>
52   * @author <a href="mailto:paulo.gaspar@krankikom.de">Paulo Gaspar</a>
53   * @version $Id: IntrospectorBase.java,v 1.3 2004/02/28 13:45:21 yoavs Exp $
54   */
55  public class IntrospectorBase
56  {   
57      /***
58       * Holds the method maps for the classes we know about, keyed by
59       * Class object.
60       */ 
61      protected  Map classMethodMaps = new HashMap();
62      
63      /***
64       * Holds the qualified class names for the classes
65       * we hold in the classMethodMaps hash
66       */
67      protected Set cachedClassNames = new HashSet();
68     
69      /***
70       * Gets the method defined by <code>name</code> and
71       * <code>params</code> for the Class <code>c</code>.
72       *
73       * @param c Class in which the method search is taking place
74       * @param name Name of the method being searched for
75       * @param params An array of Objects (not Classes) that describe the
76       *               the parameters
77       *
78       * @return The desired Method object.
79       */
80      public Method getMethod(Class c, String name, Object[] params)
81          throws Exception
82      {
83          if (c == null)
84          {
85              throw new Exception ( 
86                  "Introspector.getMethod(): Class method key was null: " + name );
87          }                
88  
89          ClassMap classMap = null;
90          
91          synchronized(classMethodMaps)
92          {
93              classMap = (ClassMap)classMethodMaps.get(c);
94            
95              /*
96               *  if we don't have this, check to see if we have it
97               *  by name.  if so, then we have a classloader change
98               *  so dump our caches.
99               */
100              
101             if (classMap == null)
102             {                
103                 if ( cachedClassNames.contains( c.getName() ))
104                 {
105                     /*
106                      * we have a map for a class with same name, but not
107                      * this class we are looking at.  This implies a 
108                      * classloader change, so dump
109                      */
110                     clearCache();                    
111                 }
112                  
113                 classMap = createClassMap(c);
114             }
115         }
116         
117         return classMap.findMethod(name, params);
118     }
119 
120     /***
121      * Creates a class map for specific class and registers it in the
122      * cache.  Also adds the qualified name to the name->class map
123      * for later Classloader change detection.
124      */
125     protected ClassMap createClassMap(Class c)
126     {        
127         ClassMap classMap = new ClassMap( c );        
128         classMethodMaps.put(c, classMap);
129         cachedClassNames.add( c.getName() );
130 
131         return classMap;
132     }
133 
134     /***
135      * Clears the classmap and classname
136      * caches
137      */
138     protected void clearCache()
139     {
140         /*
141          *  since we are synchronizing on this
142          *  object, we have to clear it rather than
143          *  just dump it.
144          */            
145         classMethodMaps.clear();
146         
147         /*
148          * for speed, we can just make a new one
149          * and let the old one be GC'd
150          */
151         cachedClassNames = new HashSet();
152     }
153 }