code: /* LanguageTool, a natural language style checker 
   * Copyright (C) 2014 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;
  
  import org.apache.lucene.document.Document;
  import org.apache.lucene.index.DirectoryReader;
  import org.apache.lucene.index.Term;
  import org.apache.lucene.search.IndexSearcher;
  import org.apache.lucene.search.Query;
  import org.apache.lucene.search.ScoreDoc;
  import org.apache.lucene.search.TermQuery;
  import org.apache.lucene.store.FSDirectory;
  import org.junit.Ignore;
  import org.junit.Test;
  
  import java.io.File;
  import java.io.IOException;
  import java.util.Scanner;
  
  public class FrequencyIndexCreatorTest {
  
    private static final File INDEX_DIR = new File("/media/Data/google-ngram/3gram/lucene-index");
  
    @Test
    @Ignore("Interactive use only")
    public void testReadPerformance() throws IOException {
      try (FSDirectory directory = FSDirectory.open(INDEX_DIR.toPath())) {
        DirectoryReader reader = DirectoryReader.open(directory);
        IndexSearcher searcher = new IndexSearcher(reader);
        try (Scanner scanner = new Scanner(new File("/lt/performance-test/en.txt"))) {
          while (scanner.hasNextLine()) {
            String line = scanner.nextLine();
            String[] parts = line.split(" ");
            accessNgrams(parts, searcher);
          }
        }
      }
    }
  
    private void accessNgrams(String[] parts, IndexSearcher searcher) throws IOException {
      String prevPart = null;
      String prevPrevPart = null;
      for (String part : parts) {
        if (prevPart != null && prevPrevPart != null) {
          String ngram = prevPrevPart + " " + prevPart + " " + part;
          long startTime = System.currentTimeMillis(); 
          Query query = new TermQuery(new Term("ngram", ngram));
          ScoreDoc[] hits = searcher.search(query, 10).scoreDocs;
          //if (hits.length == 0) {
          //  System.out.println("No hit for: " + ngram);
          //}
          for (ScoreDoc hit : hits) {
            Document hitDoc = searcher.doc(hit.doc);
            long runTime = System.currentTimeMillis() - startTime;
            System.out.println(ngram + ": " + hitDoc.getField("count").stringValue() + " (" + runTime + "ms)");
          }
        }
        prevPrevPart = prevPart;
        prevPart = part;
      }
    }
  }
  