FacetTokenizer.java

package org.cdlib.xtf.textIndexer;


/*
 * Copyright (c) 2005, Regents of the University of California
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 * - 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.
 * - Neither the name of the University of California nor the names of its
 *   contributors may be used to endorse or promote products derived from this
 *   software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS 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 THE COPYRIGHT OWNER OR 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.
 */
import java.io.IOException;
import org.apache.lucene.analysis.Token;
import org.apache.lucene.analysis.TokenStream;

/*
 * This file created on Apr 14, 2005 by Martin Haye
 */

/**
 * Performs special tokenization for facet fields. Looks for the hierarchy
 * marker "::" between hierarchy levels. For instance, the string
 * "US::California::Alameda County::Berkeley" would be made into four tokens:
 *
 *    US
 *    US::California
 *    US::California::Alameda County
 *    US::California::Alameda County::Berkeley
 *
 * @author Martin Haye
 */
public class FacetTokenizer extends TokenStream 
{
  String str;
  int pos = 0;
  Token nextToken = null;

  /**
   * Construct a token stream to remove accents from the input tokens.
   *
   * @param str   The string to tokenize
   */
  public FacetTokenizer(String str) {
    this.str = str;
  } // constructor

  /** Retrieve the next token in the stream. */
  public Token next()
    throws IOException 
  {
    Token t;

    // Do we have a queued token? If so, return it.
    if (nextToken != null) 
    {
      t = nextToken;
      nextToken = null;
    }
    else {
      // Are we at the end? If so, tell the caller.
      if (pos > str.length())
        return null;

      // Find the next divider. If not found, eat everything to the end.
      pos = str.indexOf("::", pos);
      if (pos < 0)
        pos = str.length();

      // Grab the string, and un-do the temporary escaping of XML-special
      // characters.
      //
      String term = str.substring(0, pos);
      term = term.replace("<", "<");
      term = term.replace(">", ">");
      term = term.replace("&", "&");
      
      // Form the new token and advance.
      t = new Token(term, 0, pos);
      pos += 2;

      // If the lower-case version is different, queue that token as well.
      // That way queries will work properly.
      //
      String lcTerm = term.toLowerCase();
      if (!lcTerm.equals(term))
        nextToken = new Token(lcTerm, 0, pos);
    }
    return t;
  } // next()
} // class FacetTokenizer