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1   package org.apache.commons.digester3.plugins.strategies;
2   
3   /*
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *   http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing,
15   * software distributed under the License is distributed on an
16   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17   * KIND, either express or implied.  See the License for the
18   * specific language governing permissions and limitations
19   * under the License.
20   */
21  
22  import java.util.Properties;
23  import java.lang.reflect.Method;
24  
25  import org.apache.commons.digester3.Digester;
26  import org.apache.commons.digester3.plugins.PluginException;
27  import org.apache.commons.digester3.plugins.RuleFinder;
28  import org.apache.commons.digester3.plugins.RuleLoader;
29  
30  /**
31   * A rule-finding algorithm which looks for a method with a specific name on the plugin class.
32   * 
33   * @since 1.6
34   */
35  public class FinderFromDfltMethod
36      extends RuleFinder
37  {
38      private static final String DFLT_METHOD_NAME = "addRules";
39  
40      private final String methodName;
41  
42      /** See {@link #findLoader}. */
43      public FinderFromDfltMethod()
44      {
45          this( DFLT_METHOD_NAME );
46      }
47  
48      /**
49       * Create a rule-finder which invokes a specific method on the plugin class whenever dynamic rules for a plugin need
50       * to be loaded. See the findRules method for more info.
51       * 
52       * @param methodName must be non-null.
53       */
54      public FinderFromDfltMethod( String methodName )
55      {
56          this.methodName = methodName;
57      }
58  
59      /**
60       * If there exists on the plugin class a method with name matching the constructor's methodName value then locate
61       * the appropriate Method on the plugin class and return an object encapsulating that info.
62       * <p>
63       * If there is no matching method then just return null.
64       * <p>
65       * The returned object (when non-null) will invoke the target method on the plugin class whenever its addRules
66       * method is invoked. The target method is expected to have the following prototype:
67       * <code> public static void xxxxx(Digester d, String patternPrefix); </code>
68       *
69       * @param d The digester instance where locating plugin classes
70       * @param pluginClass The plugin Java class
71       * @param p The properties object that holds any xml attributes the user may have specified on the plugin
72       *          declaration in order to indicate how to locate the plugin rules.
73       * @return a source of digester rules for the specified plugin class.
74       * @throws PluginException if the algorithm finds a source of rules, but there is something invalid
75       *         about that source.
76       */
77      @Override
78      public RuleLoader findLoader( Digester d, Class<?> pluginClass, Properties p )
79          throws PluginException
80      {
81  
82          Method rulesMethod = LoaderFromClass.locateMethod( pluginClass, methodName );
83          if ( rulesMethod == null )
84          {
85              return null;
86          }
87  
88          return new LoaderFromClass( pluginClass, rulesMethod );
89      }
90  
91  }