standardfilter.java

Lucene a java open-source SearchEngine Framework

package org.apache.lucene.analysis.standard;

/**
 * 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.
 */

import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.Token;
import org.apache.lucene.analysis.TokenStream;

/** Normalizes tokens extracted with {@link StandardTokenizer}. */

public final class StandardFilter extends TokenFilter {


  /** Construct filtering <i>in</i>. */
  public StandardFilter(TokenStream in) {
    super(in);
  }

  private static final String APOSTROPHE_TYPE = StandardTokenizerImpl.TOKEN_TYPES[StandardTokenizerImpl.APOSTROPHE];
  private static final String ACRONYM_TYPE = StandardTokenizerImpl.TOKEN_TYPES[StandardTokenizerImpl.ACRONYM];

  /** Returns the next token in the stream, or null at EOS.
   * <p>Removes <tt>'s</tt> from the end of words.
   * <p>Removes dots from acronyms.
   */
  public final Token next(Token result) throws java.io.IOException {
    Token t = input.next(result);

    if (t == null)
      return null;

    char[] buffer = t.termBuffer();
    final int bufferLength = t.termLength();
    final String type = t.type();

    if (type == APOSTROPHE_TYPE &&		  // remove 's
	bufferLength >= 2 &&
        buffer[bufferLength-2] == '\'' &&
        (buffer[bufferLength-1] == 's' || buffer[bufferLength-1] == 'S')) {
      // Strip last 2 characters off
      t.setTermLength(bufferLength - 2);
    } else if (type == ACRONYM_TYPE) {		  // remove dots
      int upto = 0;
      for(int i=0;i<bufferLength;i++) {
        char c = buffer[i];
        if (c != '.')
          buffer[upto++] = c;
      }
      t.setTermLength(upto);
    }

    return t;
  }
}