/*
    * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
    *
    * This software is open source.
    * See the bottom of this file for the licence.
    */
   
   package org.dom4j.tree;
   
  import java.lang.ref.WeakReference;
  import java.lang.reflect.Constructor;
  import java.util.Map;
  
  import org.dom4j.Namespace;
  
  /***
   * <p>
   * <code>NamespaceCache</code> caches instances of
   * <code>DefaultNamespace</code> for reuse both across documents and within
   * documents.
   * </p>
   * 
   * @author <a href="mailto:james.strachan@metastuff.com">James Strachan </a>
   * @author Maarten Coene
   * @author Brett Finnell
   * @version $Revision: 1.15 $
   */
  public class NamespaceCache {
      private static final String CONCURRENTREADERHASHMAP_CLASS
              = "EDU.oswego.cs.dl.util.concurrent.ConcurrentReaderHashMap";
  
      /***
       * Cache of {@link Map}instances indexed by URI which contain caches of
       * {@link Namespace}for each prefix
       */
      protected static Map cache;
  
      /***
       * Cache of {@link Namespace}instances indexed by URI for default
       * namespaces with no prefixes
       */
      protected static Map noPrefixCache;
  
      static {
          /* Try the java.util.concurrent.ConcurrentHashMap first. */
          try {
              Class clazz = Class
                      .forName("java.util.concurrent.ConcurrentHashMap");
              Constructor construct = clazz.getConstructor(new Class[] {
                      Integer.TYPE, Float.TYPE, Integer.TYPE });
              cache = (Map) construct.newInstance(new Object[] {new Integer(11),
                      new Float(0.75f), new Integer(1) });
              noPrefixCache = (Map) construct.newInstance(new Object[] {
                      new Integer(11), new Float(0.75f), new Integer(1) });
          } catch (Throwable t1) {
              /* Try to use the util.concurrent library (if in classpath) */
              try {
                  Class clazz = Class.forName(CONCURRENTREADERHASHMAP_CLASS);
                  cache = (Map) clazz.newInstance();
                  noPrefixCache = (Map) clazz.newInstance();
              } catch (Throwable t2) {
                  /* If previous implementations fail, use internal one */
                  cache = new ConcurrentReaderHashMap();
                  noPrefixCache = new ConcurrentReaderHashMap();
              }
          }
      }
  
      /***
       * DOCUMENT ME!
       * 
       * @param prefix
       *            DOCUMENT ME!
       * @param uri
       *            DOCUMENT ME!
       * 
       * @return the namespace for the given prefix and uri
       */
      public Namespace get(String prefix, String uri) {
          Map uriCache = getURICache(uri);
          WeakReference ref = (WeakReference) uriCache.get(prefix);
          Namespace answer = null;
  
          if (ref != null) {
              answer = (Namespace) ref.get();
          }
  
          if (answer == null) {
              synchronized (uriCache) {
                  ref = (WeakReference) uriCache.get(prefix);
  
                  if (ref != null) {
                      answer = (Namespace) ref.get();
                  }
  
                  if (answer == null) {
                      answer = createNamespace(prefix, uri);
                      uriCache.put(prefix, new WeakReference(answer));
                  }
             }
         }
 
         return answer;
     }
 
     /***
      * DOCUMENT ME!
      * 
      * @param uri
      *            DOCUMENT ME!
      * 
      * @return the name model for the given name and namepsace
      */
     public Namespace get(String uri) {
         WeakReference ref = (WeakReference) noPrefixCache.get(uri);
         Namespace answer = null;
 
         if (ref != null) {
             answer = (Namespace) ref.get();
         }
 
         if (answer == null) {
             synchronized (noPrefixCache) {
                 ref = (WeakReference) noPrefixCache.get(uri);
 
                 if (ref != null) {
                     answer = (Namespace) ref.get();
                 }
 
                 if (answer == null) {
                     answer = createNamespace("", uri);
                     noPrefixCache.put(uri, new WeakReference(answer));
                 }
             }
         }
 
         return answer;
     }
 
     /***
      * DOCUMENT ME!
      * 
      * @param uri
      *            DOCUMENT ME!
      * 
      * @return the cache for the given namespace URI. If one does not currently
      *         exist it is created.
      */
     protected Map getURICache(String uri) {
         Map answer = (Map) cache.get(uri);
 
         if (answer == null) {
             synchronized (cache) {
                 answer = (Map) cache.get(uri);
 
                 if (answer == null) {
                     answer = new ConcurrentReaderHashMap();
                     cache.put(uri, answer);
                 }
             }
         }
 
         return answer;
     }
 
     /***
      * A factory method to create {@link Namespace}instance
      * 
      * @param prefix
      *            DOCUMENT ME!
      * @param uri
      *            DOCUMENT ME!
      * 
      * @return a newly created {@link Namespace}instance.
      */
     protected Namespace createNamespace(String prefix, String uri) {
         return new Namespace(prefix, uri);
     }
 }
 
 /*
  * Redistribution and use of this software and associated documentation
  * ("Software"), with or without modification, are permitted provided that the
  * following conditions are met:
  * 
  * 1. Redistributions of source code must retain copyright statements and
  * notices. Redistributions must also contain a copy of this document.
  * 
  * 2. Redistributions in binary form must reproduce the above copyright notice,
  * this list of conditions and the following disclaimer in the documentation
  * and/or other materials provided with the distribution.
  * 
  * 3. The name "DOM4J" must not be used to endorse or promote products derived
  * from this Software without prior written permission of MetaStuff, Ltd. For
  * written permission, please contact dom4j-info@metastuff.com.
  * 
  * 4. Products derived from this Software may not be called "DOM4J" nor may
  * "DOM4J" appear in their names without prior written permission of MetaStuff,
  * Ltd. DOM4J is a registered trademark of MetaStuff, Ltd.
  * 
  * 5. Due credit should be given to the DOM4J Project - http://www.dom4j.org
  * 
  * THIS SOFTWARE IS PROVIDED BY METASTUFF, LTD. AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED. IN NO EVENT SHALL METASTUFF, LTD. OR ITS CONTRIBUTORS BE
  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  * 
  * Copyright 2001-2005 (C) MetaStuff, Ltd. All Rights Reserved.
  */