Lucene example source code file (PrefixAwareTokenFilter.java)

This example Lucene source code file (PrefixAwareTokenFilter.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

chartermattribute, io, ioexception, ioexception, offsetattribute, override, override, payloadattribute, positionincrementattribute, prefixawaretokenfilter, token, token, tokenstream, tokenstream, typeattribute

The Lucene PrefixAwareTokenFilter.java source code

package org.apache.lucene.analysis.miscellaneous;

/**
 * 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.Token;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.FlagsAttribute;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.analysis.tokenattributes.PayloadAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.TypeAttribute;
import org.apache.lucene.index.Payload;

import java.io.IOException;


/**
 * Joins two token streams and leaves the last token of the first stream available
 * to be used when updating the token values in the second stream based on that token.
 *
 * The default implementation adds last prefix token end offset to the suffix token start and end offsets.
 * <p/>
 * <b>NOTE: This filter might not behave correctly if used with custom Attributes, i.e. Attributes other than
 * the ones located in org.apache.lucene.analysis.tokenattributes. 
 */
public class PrefixAwareTokenFilter extends TokenStream {

  private TokenStream prefix;
  private TokenStream suffix;
  
  private CharTermAttribute termAtt;
  private PositionIncrementAttribute posIncrAtt;
  private PayloadAttribute payloadAtt;
  private OffsetAttribute offsetAtt;
  private TypeAttribute typeAtt;
  private FlagsAttribute flagsAtt;

  private CharTermAttribute p_termAtt;
  private PositionIncrementAttribute p_posIncrAtt;
  private PayloadAttribute p_payloadAtt;
  private OffsetAttribute p_offsetAtt;
  private TypeAttribute p_typeAtt;
  private FlagsAttribute p_flagsAtt;

  public PrefixAwareTokenFilter(TokenStream prefix, TokenStream suffix) {
    super(suffix);
    this.suffix = suffix;
    this.prefix = prefix;
    prefixExhausted = false;
    
    termAtt = addAttribute(CharTermAttribute.class);
    posIncrAtt = addAttribute(PositionIncrementAttribute.class);
    payloadAtt = addAttribute(PayloadAttribute.class);
    offsetAtt = addAttribute(OffsetAttribute.class);
    typeAtt = addAttribute(TypeAttribute.class);
    flagsAtt = addAttribute(FlagsAttribute.class);

    p_termAtt = prefix.addAttribute(CharTermAttribute.class);
    p_posIncrAtt = prefix.addAttribute(PositionIncrementAttribute.class);
    p_payloadAtt = prefix.addAttribute(PayloadAttribute.class);
    p_offsetAtt = prefix.addAttribute(OffsetAttribute.class);
    p_typeAtt = prefix.addAttribute(TypeAttribute.class);
    p_flagsAtt = prefix.addAttribute(FlagsAttribute.class);
  }

  private Token previousPrefixToken = new Token();
  private Token reusableToken = new Token();

  private boolean prefixExhausted;

  @Override
  public final boolean incrementToken() throws IOException {
    if (!prefixExhausted) {
      Token nextToken = getNextPrefixInputToken(reusableToken);
      if (nextToken == null) {
        prefixExhausted = true;
      } else {
        previousPrefixToken.reinit(nextToken);
        // Make it a deep copy
        Payload p = previousPrefixToken.getPayload();
        if (p != null) {
          previousPrefixToken.setPayload((Payload) p.clone());
        }
        setCurrentToken(nextToken);
        return true;
      }
    }

    Token nextToken = getNextSuffixInputToken(reusableToken);
    if (nextToken == null) {
      return false;
    }

    nextToken = updateSuffixToken(nextToken, previousPrefixToken);
    setCurrentToken(nextToken);
    return true;
  }
  
  private void setCurrentToken(Token token) {
    if (token == null) return;
    clearAttributes();
    termAtt.copyBuffer(token.buffer(), 0, token.length());
    posIncrAtt.setPositionIncrement(token.getPositionIncrement());
    flagsAtt.setFlags(token.getFlags());
    offsetAtt.setOffset(token.startOffset(), token.endOffset());
    typeAtt.setType(token.type());
    payloadAtt.setPayload(token.getPayload());
  }
  
  private Token getNextPrefixInputToken(Token token) throws IOException {
    if (!prefix.incrementToken()) return null;
    token.copyBuffer(p_termAtt.buffer(), 0, p_termAtt.length());
    token.setPositionIncrement(p_posIncrAtt.getPositionIncrement());
    token.setFlags(p_flagsAtt.getFlags());
    token.setOffset(p_offsetAtt.startOffset(), p_offsetAtt.endOffset());
    token.setType(p_typeAtt.type());
    token.setPayload(p_payloadAtt.getPayload());
    return token;
  }

  private Token getNextSuffixInputToken(Token token) throws IOException {
    if (!suffix.incrementToken()) return null;
    token.copyBuffer(termAtt.buffer(), 0, termAtt.length());
    token.setPositionIncrement(posIncrAtt.getPositionIncrement());
    token.setFlags(flagsAtt.getFlags());
    token.setOffset(offsetAtt.startOffset(), offsetAtt.endOffset());
    token.setType(typeAtt.type());
    token.setPayload(payloadAtt.getPayload());
    return token;
  }

  /**
   * The default implementation adds last prefix token end offset to the suffix token start and end offsets.
   *
   * @param suffixToken a token from the suffix stream
   * @param lastPrefixToken the last token from the prefix stream
   * @return consumer token
   */
  public Token updateSuffixToken(Token suffixToken, Token lastPrefixToken) {
    suffixToken.setStartOffset(lastPrefixToken.endOffset() + suffixToken.startOffset());
    suffixToken.setEndOffset(lastPrefixToken.endOffset() + suffixToken.endOffset());
    return suffixToken;
  }

  @Override
  public void end() throws IOException {
    prefix.end();
    suffix.end();
  }

  @Override
  public void close() throws IOException {
    prefix.close();
    suffix.close();
  }

  @Override
  public void reset() throws IOException {
    super.reset();
    if (prefix != null) {
      prefixExhausted = false;
      prefix.reset();
    }
    if (suffix != null) {
      suffix.reset();
    }


  }

  public TokenStream getPrefix() {
    return prefix;
  }

  public void setPrefix(TokenStream prefix) {
    this.prefix = prefix;
  }

  public TokenStream getSuffix() {
    return suffix;
  }

  public void setSuffix(TokenStream suffix) {
    this.suffix = suffix;
  }
}