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1   package org.apache.velocity.anakia;
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 com.werken.xpath.XPath;
23  import java.util.Map;
24  import java.util.WeakHashMap;
25  
26  /**
27   * Provides a cache for XPath expressions. Used by {@link NodeList} and
28   * {@link AnakiaElement} to minimize XPath parsing in their
29   * <code>selectNodes()</code> methods.
30   *
31   * @author <a href="mailto:szegedia@freemail.hu">Attila Szegedi</a>
32   * @version $Id: XPathCache.java 463298 2006-10-12 16:10:32Z henning $
33   */
34  class XPathCache
35  {
36      // Cache of already parsed XPath expressions, keyed by String representations
37      // of the expression as passed to getXPath().
38      private static final Map XPATH_CACHE = new WeakHashMap();
39  
40      private XPathCache()
41      {
42      }
43  
44      /**
45       * Returns an XPath object representing the requested XPath expression.
46       * A cached object is returned if it already exists for the requested expression.
47       * @param xpathString the XPath expression to parse
48       * @return the XPath object that represents the parsed XPath expression.
49       */
50      static XPath getXPath(String xpathString)
51      {
52          XPath xpath = null;
53          synchronized(XPATH_CACHE)
54          {
55              xpath = (XPath)XPATH_CACHE.get(xpathString);
56              if(xpath == null)
57              {
58                  xpath = new XPath(xpathString);
59                  XPATH_CACHE.put(xpathString, xpath);
60              }
61          }
62          return xpath;
63      }
64  }