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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  import java.util.Map;
20  import java.util.Set;
21  import java.util.HashMap;
22  import java.util.HashSet;
23  
24  import java.lang.reflect.Method;
25  
26  /***
27   * This basic function of this class is to return a Method object for a
28   * particular class given the name of a method and the parameters to the method
29   * in the form of an Object[]
30   * 
31   * The first time the Introspector sees a class it creates a class method map
32   * for the class in question. Basically the class method map is a Hastable where
33   * Method objects are keyed by a concatenation of the method name and the names
34   * of classes that make up the parameters.
35   * 
36   * For example, a method with the following signature:
37   * 
38   * public void method(String a, StringBuffer b)
39   * 
40   * would be mapped by the key:
41   * 
42   * "method" + "java.lang.String" + "java.lang.StringBuffer"
43   * 
44   * This mapping is performed for all the methods in a class and stored for
45   * 
46   * @since 1.0
47   * @author <a href="mailto:jvanzyl@apache.org">Jason van Zyl</a>
48   * @author <a href="mailto:bob@werken.com">Bob McWhirter</a>
49   * @author <a href="mailto:szegedia@freemail.hu">Attila Szegedi</a>
50   * @author <a href="mailto:paulo.gaspar@krankikom.de">Paulo Gaspar</a>
51   * @version $Id: IntrospectorBase.java 398464 2006-04-30 23:50:43Z dion $
52   */
53  public class IntrospectorBase {
54      /***
55       * Holds the method maps for the classes we know about, keyed by Class
56       * object.
57       */
58      protected Map classMethodMaps = new HashMap();
59  
60      /***
61       * Holds the qualified class names for the classes we hold in the
62       * classMethodMaps hash.
63       */
64      protected Set cachedClassNames = new HashSet();
65  
66      /***
67       * Gets the method defined by <code>name</code> and <code>params</code>
68       * for the Class <code>c</code>.
69       * 
70       * @param c Class in which the method search is taking place
71       * @param name Name of the method being searched for
72       * @param params An array of Objects (not Classes) that describe the the
73       *            parameters
74       * 
75       * @return The desired Method object.
76       * @throws Exception on any logical error.
77       */
78      public Method getMethod(Class c, String name, Object[] params) throws Exception {
79          if (c == null) {
80              throw new Exception("Introspector.getMethod(): Class method key was null: " + name);
81          }
82  
83          ClassMap classMap = null;
84  
85          synchronized (classMethodMaps) {
86              classMap = (ClassMap) classMethodMaps.get(c);
87  
88              /*
89               * if we don't have this, check to see if we have it by name. if so,
90               * then we have a classloader change so dump our caches.
91               */
92  
93              if (classMap == null) {
94                  if (cachedClassNames.contains(c.getName())) {
95                      /*
96                       * we have a map for a class with same name, but not this
97                       * class we are looking at. This implies a classloader
98                       * change, so dump
99                       */
100                     clearCache();
101                 }
102 
103                 classMap = createClassMap(c);
104             }
105         }
106 
107         return classMap.findMethod(name, params);
108     }
109 
110     /***
111      * Creates a class map for specific class and registers it in the cache.
112      * Also adds the qualified name to the name->class map for later Classloader
113      * change detection.
114      * @param c class.
115      * @return a {@link ClassMap}
116      */
117     protected ClassMap createClassMap(Class c) {
118         ClassMap classMap = new ClassMap(c);
119         classMethodMaps.put(c, classMap);
120         cachedClassNames.add(c.getName());
121 
122         return classMap;
123     }
124 
125     /***
126      * Clears the classmap and classname caches.
127      */
128     protected void clearCache() {
129         /*
130          * since we are synchronizing on this object, we have to clear it rather
131          * than just dump it.
132          */
133         classMethodMaps.clear();
134 
135         /*
136          * for speed, we can just make a new one and let the old one be GC'd
137          */
138         cachedClassNames = new HashSet();
139     }
140 }