code: /* LanguageTool, a natural language style checker
   * Copyright (C) 2021 Daniel Naber (http://www.danielnaber.de)
   *
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
   * USA
   */
  package org.languagetool.dev.bigdata;
  
  import org.apache.lucene.document.Document;
  import org.apache.lucene.index.DirectoryReader;
  import org.apache.lucene.store.Directory;
  import org.apache.lucene.store.SimpleFSDirectory;
  
  import java.io.IOException;
  import java.nio.file.Paths;
  
  /**
   * Export the sentences of a Lucene index.
   */
  public class LuceneIndexExporter {
  
    private static final String FIELD_NAME = "fieldLowercase";
  
    public static void main(String[] args) throws IOException {
      if (args.length != 1) {
        System.out.println("Usage: " + LuceneIndexExporter.class.getSimpleName() + " <luceneIndexDir>");
        System.exit(1);
      }
      System.out.println("Using field: " + FIELD_NAME);
      Directory directory = SimpleFSDirectory.open(Paths.get(args[0]));
      try (DirectoryReader indexReader = DirectoryReader.open(directory)) {
        for (int i = 0; i < indexReader.maxDoc(); i++) {
          Document doc = indexReader.document(i);
          System.out.println(doc.get(FIELD_NAME));
        }
      }
    }
  }
  