SAXConfigurationHandler


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55  package org.apache.avalon.framework.configuration;
56  
57  import java.util.ArrayList  ;
58  import java.util.BitSet  ;
59  import org.xml.sax.Attributes  ;
60  import org.xml.sax.ErrorHandler  ;
61  import org.xml.sax.Locator  ;
62  import org.xml.sax.SAXException  ;
63  import org.xml.sax.SAXParseException  ;
64  import org.xml.sax.helpers.DefaultHandler  ;
65  
66  /**
67   * A SAXConfigurationHandler helps build Configurations out of sax events.
68   *
69   * @author <a HREF="mailto:dev@avalon.apache.org">Avalon Development Team</a>
70   * @version CVS $Revision: 1.29 $ $Date: 2003/02/11 15:58:39 $
71   */
72  public class SAXConfigurationHandler
73      extends DefaultHandler  
74      implements ErrorHandler  
75  {
76      /**
77       * Likely number of nested configuration items. If more is
78       * encountered the lists will grow automatically.
79       */
80      private static final int EXPECTED_DEPTH = 5;
81      private final ArrayList   m_elements = new ArrayList  ( EXPECTED_DEPTH );
82      private final ArrayList   m_values = new ArrayList  ( EXPECTED_DEPTH );
83      /**
84       * Contains true at index n if space in the configuration with
85       * depth n is to be preserved.
86       */
87      private final BitSet   m_preserveSpace = new BitSet  ();
88      private Configuration m_configuration;
89      private Locator   m_locator;
90  
91      /**
92       * Get the configuration object that was built.
93       *
94       * @return a <code>Configuration</code> object
95       */
96      public Configuration getConfiguration()
97      {
98          return m_configuration;
99      }
100 
101     /**
102      * Clears all data from this configuration handler.
103      */
104     public void clear()
105     {
106         m_elements.clear();
107         m_values.clear();
108         m_locator = null;
109     }
110 
111     /**
112      * Set the document <code>Locator</code> to use.
113      *
114      * @param locator a <code>Locator</code> value
115      */
116     public void setDocumentLocator( final Locator   locator )
117     {
118         m_locator = locator;
119     }
120 
121     /**
122      * Handling hook for character data.
123      *
124      * @param ch a <code>char[]</code> of data
125      * @param start offset in the character array from which to start reading
126      * @param end length of character data
127      * @throws SAXException if an error occurs
128      */
129     public void characters( final char[] ch, int start, int end )
130         throws SAXException  
131     {
132         // it is possible to play micro-optimization here by doing
133         // manual trimming and thus preserve some precious bits
134         // of memory, but it's really not important enough to justify
135         // resulting code complexity
136         final int depth = m_values.size() - 1;
137         final StringBuffer   valueBuffer = (StringBuffer  )m_values.get( depth );
138         valueBuffer.append( ch, start, end );
139     }
140 
141     /**
142      * Handling hook for finishing parsing of an element.
143      *
144      * @param namespaceURI a <code>String</code> value
145      * @param localName a <code>String</code> value
146      * @param rawName a <code>String</code> value
147      * @throws SAXException if an error occurs
148      */
149     public void endElement( final String   namespaceURI,
150                             final String   localName,
151                             final String   rawName )
152         throws SAXException  
153     {
154         final int depth = m_elements.size() - 1;
155         final DefaultConfiguration finishedConfiguration =
156             (DefaultConfiguration)m_elements.remove( depth );
157         final String   accumulatedValue =
158             ( (StringBuffer  )m_values.remove( depth ) ).toString();
159 
160         if( finishedConfiguration.getChildren().length == 0 )
161         {
162             // leaf node
163             String   finishedValue;
164             if( m_preserveSpace.get( depth ) )
165             {
166                 finishedValue = accumulatedValue;
167             }
168             else if( 0 == accumulatedValue.length() )
169             {
170                 finishedValue = null;
171             }
172             else
173             {
174                 finishedValue = accumulatedValue.trim();
175             }
176             finishedConfiguration.setValue( finishedValue );
177         }
178         else
179         {
180             final String   trimmedValue = accumulatedValue.trim();
181             if( trimmedValue.length() > 0 )
182             {
183                 throw new SAXException  ( "Not allowed to define mixed content in the "
184                                         + "element " + finishedConfiguration.getName() + " at "
185                                         + finishedConfiguration.getLocation() );
186             }
187         }
188 
189         if( 0 == depth )
190         {
191             m_configuration = finishedConfiguration;
192         }
193     }
194 
195     /**
196      * Create a new <code>DefaultConfiguration</code> with the specified
197      * local name and location.
198      *
199      * @param localName a <code>String</code> value
200      * @param location a <code>String</code> value
201      * @return a <code>DefaultConfiguration</code> value
202      */
203     protected DefaultConfiguration createConfiguration( final String   localName,
204                                                         final String   location )
205     {
206         return new DefaultConfiguration( localName, location );
207     }
208 
209     /**
210      * Handling hook for starting parsing of an element.
211      *
212      * @param namespaceURI a <code>String</code> value
213      * @param localName a <code>String</code> value
214      * @param rawName a <code>String</code> value
215      * @param attributes an <code>Attributes</code> value
216      * @throws SAXException if an error occurs
217      */
218     public void startElement( final String   namespaceURI,
219                               final String   localName,
220                               final String   rawName,
221                               final Attributes   attributes )
222         throws SAXException  
223     {
224         final DefaultConfiguration configuration =
225             createConfiguration( rawName, getLocationString() );
226         // depth of new configuration (not decrementing here, configuration
227         // is to be added)
228         final int depth = m_elements.size();
229         boolean preserveSpace = false; // top level element trims space by default
230 
231         if( depth > 0 )
232         {
233             final DefaultConfiguration parent =
234                 (DefaultConfiguration)m_elements.get( depth - 1 );
235             parent.addChild( configuration );
236             // inherits parent's space preservation policy
237             preserveSpace = m_preserveSpace.get( depth - 1 );
238         }
239 
240         m_elements.add( configuration );
241         m_values.add( new StringBuffer  () );
242 
243         final int attributesSize = attributes.getLength();
244 
245         for( int i = 0; i < attributesSize; i++ )
246         {
247             final String   name = attributes.getQName( i );
248             final String   value = attributes.getValue( i );
249 
250             if( !name.equals( "xml:space" ) )
251             {
252                 configuration.setAttribute( name, value );
253             }
254             else
255             {
256                 preserveSpace = value.equals( "preserve" );
257             }
258         }
259 
260         if( preserveSpace )
261         {
262             m_preserveSpace.set( depth );
263         }
264         else
265         {
266             m_preserveSpace.clear( depth );
267         }
268     }
269 
270     /**
271      * This just throws an exception on a parse error.
272      * @param exception the parse error
273      * @throws SAXException if an error occurs
274      */
275     public void error( final SAXParseException   exception )
276         throws SAXException  
277     {
278         throw exception;
279     }
280 
281     /**
282      * This just throws an exception on a parse error.
283      * @param exception the parse error
284      * @throws SAXException if an error occurs
285      */
286     public void warning( final SAXParseException   exception )
287         throws SAXException  
288     {
289         throw exception;
290     }
291 
292     /**
293      * This just throws an exception on a parse error.
294      * @param exception the parse error
295      * @throws SAXException if an error occurs
296      */
297     public void fatalError( final SAXParseException   exception )
298         throws SAXException  
299     {
300         throw exception;
301     }
302 
303     /**
304      * Returns a string showing the current system ID, line number and column number.
305      *
306      * @return a <code>String</code> value
307      */
308     protected String   getLocationString()
309     {
310         if( null == m_locator )
311         {
312             return "Unknown";
313         }
314         else
315         {
316             return
317                 m_locator.getSystemId() + ":"
318                 + m_locator.getLineNumber() + ":"
319                 + m_locator.getColumnNumber();
320         }
321     }
322 }
323
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