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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.configuration;
18  
19  import java.util.ArrayList;
20  import java.util.Collection;
21  import java.util.Collections;
22  import java.util.HashSet;
23  import java.util.Iterator;
24  import java.util.List;
25  import java.util.Set;
26  
27  /***
28   * <p>A base class for converters that transform a normal configuration
29   * object into a hierarchical configuration.</p>
30   * <p>This class provides a default mechanism for iterating over the keys in a
31   * configuration and to throw corresponding element start and end events. By
32   * handling these events a hierarchy can be constructed that is equivalent to
33   * the keys in the original configuration.</p>
34   * <p>Concrete sub classes will implement event handlers that generate SAX
35   * events for XML processing or construct a
36   * <code>HierarchicalConfiguration</code> root node. All in all with this class
37   * it is possible to treat a default configuration as if it was a hierarchical
38   * configuration, which can be sometimes useful.</p>
39   * @see HierarchicalConfiguration
40   *
41   * @author <a href="mailto:oliver.heger@t-online.de">Oliver Heger</a>
42   * @version $Id: HierarchicalConfigurationConverter.java 155408 2005-02-26 12:56:39Z dirkv $
43   */
44  abstract class HierarchicalConfigurationConverter
45  {
46      /***
47       * Processes the specified configuration object. This method implements
48       * the iteration over the configuration's keys. All defined keys are
49       * translated into a set of element start and end events represented by
50       * calls to the <code>elementStart()</code> and
51       * <code>elementEnd()</code> methods.
52       *
53       * @param config the configuration to be processed
54       */
55      public void process(Configuration config)
56      {
57          if (config != null)
58          {
59              ConfigurationKey keyEmpty = new ConfigurationKey();
60              ConfigurationKey keyLast = keyEmpty;
61              Set keySet = new HashSet();
62  
63              for (Iterator it = config.getKeys(); it.hasNext();)
64              {
65                  String key = (String) it.next();
66                  if (keySet.contains(key))
67                  {
68                      // this key has already been processed by openElements
69                      continue;
70                  }
71                  ConfigurationKey keyAct = new ConfigurationKey(key);
72                  closeElements(keyLast, keyAct);
73                  String elem = openElements(keyLast, keyAct, config, keySet);
74                  fireValue(elem, config.getProperty(key));
75                  keyLast = keyAct;
76              }
77  
78              // close all open
79              closeElements(keyLast, keyEmpty);
80          }
81      }
82  
83      /***
84       * An event handler method that is called when an element starts.
85       * Concrete sub classes must implement it to perform a proper event
86       * handling.
87       *
88       * @param name the name of the new element
89       * @param value the element's value; can be <b>null</b> if the element
90       * does not have any value
91       */
92      protected abstract void elementStart(String name, Object value);
93  
94      /***
95       * An event handler method that is called when an element ends. For each
96       * call of <code>elementStart()</code> there will be a corresponding call
97       * of this method. Concrete sub classes must implement it to perform a
98       * proper event handling.
99       *
100      * @param name the name of the ending element
101      */
102     protected abstract void elementEnd(String name);
103 
104     /***
105      * Fires all necessary element end events for the specified keys. This
106      * method is called for each key obtained from the configuration to be
107      * converted. It calculates the common part of the actual and the last
108      * processed key and thus determines how many elements must be
109      * closed.
110      *
111      * @param keyLast the last processed key
112      * @param keyAct the actual key
113      */
114     protected void closeElements(ConfigurationKey keyLast, ConfigurationKey keyAct)
115     {
116         ConfigurationKey keyDiff = keyAct.differenceKey(keyLast);
117         Iterator it = reverseIterator(keyDiff);
118         if (it.hasNext())
119         {
120             // Skip first because it has already been closed by fireValue()
121             it.next();
122         }
123 
124         while (it.hasNext())
125         {
126             elementEnd((String) it.next());
127         }
128     }
129 
130     /***
131      * Helper method for determining a reverse iterator for the specified key.
132      * This implementation returns an iterator that returns the parts of the
133      * given key in reverse order, ignoring indices.
134      *
135      * @param key the key
136      * @return a reverse iterator for the parts of this key
137      */
138     protected Iterator reverseIterator(ConfigurationKey key)
139     {
140         List list = new ArrayList();
141         for (ConfigurationKey.KeyIterator it = key.iterator(); it.hasNext();)
142         {
143             list.add(it.nextKey());
144         }
145 
146         Collections.reverse(list);
147         return list.iterator();
148     }
149 
150     /***
151      * Fires all necessary element start events for the specified key. This
152      * method is called for each key obtained from the configuration to be
153      * converted. It ensures that all elements "between" the last key and the
154      * actual key are opened and their values are set.
155      *
156      * @param keyLast the last processed key
157      * @param keyAct the actual key
158      * @param config the configuration to process
159      * @param keySet the set with the processed keys
160      * @return the name of the last element on the path
161      */
162     protected String openElements(ConfigurationKey keyLast, ConfigurationKey keyAct, Configuration config, Set keySet)
163     {
164         ConfigurationKey.KeyIterator it = keyLast.differenceKey(keyAct).iterator();
165         ConfigurationKey k = keyLast.commonKey(keyAct);
166         for (it.nextKey(); it.hasNext(); it.nextKey())
167         {
168             k.append(it.currentKey(true));
169             elementStart(it.currentKey(true), config.getProperty(k.toString()));
170             keySet.add(k.toString());
171         }
172         return it.currentKey(true);
173     }
174 
175     /***
176      * Fires all necessary element start events with the actual element values.
177      * This method is called for each key obtained from the configuration to be
178      * processed with the last part of the key as argument. The value can be
179      * either a single value or a collection.
180      *
181      * @param name the name of the actual element
182      * @param value the element's value
183      */
184     protected void fireValue(String name, Object value)
185     {
186         if (value != null && value instanceof Collection)
187         {
188             for (Iterator it = ((Collection) value).iterator(); it.hasNext();)
189             {
190                 fireValue(name, it.next());
191             }
192         }
193         else
194         {
195             elementStart(name, value);
196             elementEnd(name);
197         }
198     }
199 }