chartokenizer.java

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package org.apache.lucene.analysis;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
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 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 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 end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache Lucene" must not be used to endorse or promote products
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 * 5. Products derived from this software may not be called "Apache",
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
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import java.io.Reader;

/** An abstract base class for simple, character-oriented tokenizers.*/
public abstract class CharTokenizer extends Tokenizer {
  public CharTokenizer(Reader input) {
    this.input = input;
  }

  private int offset = 0, bufferIndex=0, dataLen=0;
  private final static int MAX_WORD_LEN = 255;
  private final static int IO_BUFFER_SIZE = 1024;
  private final char[] buffer = new char[MAX_WORD_LEN];
  private final char[] ioBuffer = new char[IO_BUFFER_SIZE];

  /** Returns true iff a character should be included in a token.  This
   * tokenizer generates as tokens adjacent sequences of characters which
   * satisfy this predicate.  Characters for which this is false are used to
   * define token boundaries and are not included in tokens. */
  protected abstract boolean isTokenChar(char c);

  /** Called on each token character to normalize it before it is added to the
   * token.  The default implementation does nothing.  Subclasses may use this
   * to, e.g., lowercase tokens. */
  protected char normalize(char c) { return c; }

  /** Returns the next token in the stream, or null at EOS. */
  public final Token next() throws java.io.IOException {
    int length = 0;
    int start = offset;
    while (true) {
      final char c;

      offset++;
      if (bufferIndex >= dataLen) {
        dataLen = input.read(ioBuffer);
        bufferIndex = 0;
      };
      if (dataLen == -1) {
	if (length > 0)
	  break;
	else
	  return null;
      }
      else
        c = (char) ioBuffer[bufferIndex++];
      
      if (isTokenChar(c)) {                       // if it's a token char

	if (length == 0)			  // start of token
	  start = offset-1;

	buffer[length++] = normalize(c);          // buffer it, normalized

	if (length == MAX_WORD_LEN)		  // buffer overflow!
	  break;

      } else if (length > 0)			  // at non-Letter w/ chars
	break;					  // return 'em

    }

    return new Token(new String(buffer, 0, length), start, start+length);
  }
}