lucene/analysis/opennlp/src/java/org/apache/lucene/analysis/opennlp/OpenNLPChunkerFilter.java

/*
 * 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.
 */

package org.apache.lucene.analysis.opennlp;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.opennlp.tools.NLPChunkerOp;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
import org.apache.lucene.analysis.tokenattributes.FlagsAttribute;
import org.apache.lucene.analysis.tokenattributes.TypeAttribute;
import org.apache.lucene.util.AttributeSource;

/**
 * Run OpenNLP chunker.  Prerequisite: the OpenNLPTokenizer and OpenNLPPOSFilter must precede this filter.
 * Tags terms in the TypeAttribute, replacing the POS tags previously put there by OpenNLPPOSFilter.
 */
public final class OpenNLPChunkerFilter extends TokenFilter {

  private List<AttributeSource> sentenceTokenAttrs = new ArrayList<>();
  private int tokenNum = 0;
  private boolean moreTokensAvailable = true;
  private String[] sentenceTerms = null;
  private String[] sentenceTermPOSTags = null;

  private final NLPChunkerOp chunkerOp;
  private final TypeAttribute typeAtt = addAttribute(TypeAttribute.class);
  private final FlagsAttribute flagsAtt = addAttribute(FlagsAttribute.class);
  private final CharTermAttribute termAtt = addAttribute(CharTermAttribute.class);

  public OpenNLPChunkerFilter(TokenStream input, NLPChunkerOp chunkerOp) {
    super(input);
    this.chunkerOp = chunkerOp;
  }

  @Override
  public final boolean incrementToken() throws IOException {
    if ( ! moreTokensAvailable) {
      clear();
      return false;
    }
    if (tokenNum == sentenceTokenAttrs.size()) {
      nextSentence();
      if (sentenceTerms == null) {
        clear();
        return false;
      }
      assignTokenTypes(chunkerOp.getChunks(sentenceTerms, sentenceTermPOSTags, null));
      tokenNum = 0;
    }
    clearAttributes();
    sentenceTokenAttrs.get(tokenNum++).copyTo(this);
    return true;
  }

  private void nextSentence() throws IOException {
    List<String> termList = new ArrayList<>();
    List<String> posTagList = new ArrayList<>();
    sentenceTokenAttrs.clear();
    boolean endOfSentence = false;
    while ( ! endOfSentence && (moreTokensAvailable = input.incrementToken())) {
      termList.add(termAtt.toString());
      posTagList.add(typeAtt.type());
      endOfSentence = 0 != (flagsAtt.getFlags() & OpenNLPTokenizer.EOS_FLAG_BIT);
      sentenceTokenAttrs.add(input.cloneAttributes());
    }
    sentenceTerms = termList.size() > 0 ? termList.toArray(new String[termList.size()]) : null;
    sentenceTermPOSTags = posTagList.size() > 0 ? posTagList.toArray(new String[posTagList.size()]) : null;
  }

  private void assignTokenTypes(String[] tags) {
    for (int i = 0 ; i < tags.length ; ++i) {
      sentenceTokenAttrs.get(i).getAttribute(TypeAttribute.class).setType(tags[i]);
    }
  }

  @Override
  public void reset() throws IOException {
    super.reset();
    moreTokensAvailable = true;
    clear();
  }

  private void clear() {
    sentenceTokenAttrs.clear();
    sentenceTerms = null;
    sentenceTermPOSTags = null;
    tokenNum = 0;
  }
}