code: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements. See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership. The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the  "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  /*
   * $Id$
   */
  
  package org.apache.xml.serializer;
  
  import java.util.Hashtable;
  
  import org.xml.sax.Attributes;
  import org.xml.sax.helpers.AttributesImpl;
  
  /**
   * This class extends org.xml.sax.helpers.AttributesImpl which implements org.
   * xml.sax.Attributes. But for optimization this class adds a Hashtable for
   * faster lookup of an index by qName, which is commonly done in the stream
   * serializer.
   * 
   * @see org.xml.sax.Attributes
   * 
   * @xsl.usage internal
   */
  public final class AttributesImplSerializer extends AttributesImpl
  {
      /**
       * Hash table of qName/index values to quickly lookup the index
       * of an attributes qName.  qNames are in uppercase in the hash table
       * to make the search case insensitive.
       * 
       * The keys to the hashtable to find the index are either
       * "prefix:localName"  or "{uri}localName".
       */
      private final Hashtable m_indexFromQName = new Hashtable();
      
      private final StringBuffer m_buff = new StringBuffer();
      
      /**
       * This is the number of attributes before switching to the hash table,
       * and can be tuned, but 12 seems good for now - Brian M.
       */
      private static final int MAX = 12;
      
      /**
       * One less than the number of attributes before switching to
       * the Hashtable.
       */
      private static final int MAXMinus1 = MAX - 1;
  
      /**
       * This method gets the index of an attribute given its qName.
       * @param qname the qualified name of the attribute, e.g. "prefix1:locName1"
       * @return the integer index of the attribute.
       * @see org.xml.sax.Attributes#getIndex(String)
       */
      public final int getIndex(String qname)
      {
          int index;
  
          if (super.getLength() < MAX)
          {
              // if we haven't got too many attributes let the
              // super class look it up
              index = super.getIndex(qname);
              return index;
          }
          // we have too many attributes and the super class is slow
          // so find it quickly using our Hashtable.
          Integer i = (Integer)m_indexFromQName.get(qname);
          if (i == null)
              index = -1;
          else
              index = i.intValue();
          return index;
      }
      /**
       * This method adds the attribute, but also records its qName/index pair in
       * the hashtable for fast lookup by getIndex(qName).
       * @param uri the URI of the attribute
       * @param local the local name of the attribute
       * @param qname the qualified name of the attribute
       * @param type the type of the attribute
       * @param val the value of the attribute
       *
       * @see org.xml.sax.helpers.AttributesImpl#addAttribute(String, String, String, String, String)
       * @see #getIndex(String)
       */
      public final void addAttribute(
          String uri,
          String local,
          String qname,
          String type,
          String val)
      {
          int index = super.getLength();
          super.addAttribute(uri, local, qname, type, val);
          // (index + 1) is now the number of attributes
          // so either compare (index+1) to MAX, or compare index to (MAX-1)
  
          if (index < MAXMinus1)
          {
              return;
          }
          else if (index == MAXMinus1)
          {
              switchOverToHash(MAX);
          }
          else
          {
              /* add the key with the format of "prefix:localName" */
              /* we have just added the attibute, its index is the old length */
              Integer i = new Integer(index);
              m_indexFromQName.put(qname, i);
              
              /* now add with key of the format "{uri}localName" */
              m_buff.setLength(0);
              m_buff.append('{').append(uri).append('}').append(local);
              String key = m_buff.toString();
              m_indexFromQName.put(key, i);
          }
          return;
      }
  
      /**
       * We are switching over to having a hash table for quick look
       * up of attributes, but up until now we haven't kept any
       * information in the Hashtable, so we now update the Hashtable.
       * Future additional attributes will update the Hashtable as
       * they are added.
       * @param numAtts
       */
      private void switchOverToHash(int numAtts)
      {
          for (int index = 0; index < numAtts; index++)
          {
              String qName = super.getQName(index);
              Integer i = new Integer(index);
              m_indexFromQName.put(qName, i);
              
              // Add quick look-up to find with uri/local name pair
              String uri = super.getURI(index);
              String local = super.getLocalName(index);
              m_buff.setLength(0);
              m_buff.append('{').append(uri).append('}').append(local);
              String key = m_buff.toString();
              m_indexFromQName.put(key, i);
          }
      }
  
      /**
       * This method clears the accumulated attributes.
       *
       * @see org.xml.sax.helpers.AttributesImpl#clear()
       */
      public final void clear()
      {
  
          int len = super.getLength();
          super.clear();
          if (MAX <= len)
          {
              // if we have had enough attributes and are
              // using the Hashtable, then clear the Hashtable too.
              m_indexFromQName.clear();
          }
  
      }
  
      /**
       * This method sets the attributes, previous attributes are cleared,
       * it also keeps the hashtable up to date for quick lookup via
       * getIndex(qName).
       * @param atts the attributes to copy into these attributes.
       * @see org.xml.sax.helpers.AttributesImpl#setAttributes(Attributes)
       * @see #getIndex(String)
       */
      public final void setAttributes(Attributes atts)
      {
  
          super.setAttributes(atts);
  
          // we've let the super class add the attributes, but
          // we need to keep the hash table up to date ourselves for the
          // potentially new qName/index pairs for quick lookup. 
          int numAtts = atts.getLength();
          if (MAX <= numAtts)
              switchOverToHash(numAtts);
  
      }
      
      /**
       * This method gets the index of an attribute given its uri and locanName.
       * @param uri the URI of the attribute name.
       * @param localName the local namer (after the ':' ) of the attribute name.
       * @return the integer index of the attribute.
       * @see org.xml.sax.Attributes#getIndex(String)
       */
      public final int getIndex(String uri, String localName)
      {
          int index;
  
          if (super.getLength() < MAX)
          {
              // if we haven't got too many attributes let the
              // super class look it up
              index = super.getIndex(uri,localName);
              return index;
          }
          // we have too many attributes and the super class is slow
          // so find it quickly using our Hashtable.
          // Form the key of format "{uri}localName"
          m_buff.setLength(0);
          m_buff.append('{').append(uri).append('}').append(localName);
          String key = m_buff.toString();
          Integer i = (Integer)m_indexFromQName.get(key);
          if (i == null)
              index = -1;
          else
              index = i.intValue();
          return index;
      }
  }
  