code: package zemberek.corpus;
  
  import java.io.IOException;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.nio.file.Paths;
  import java.util.List;
  import java.util.stream.Collectors;
  import org.apache.lucene.analysis.Analyzer;
  import org.apache.lucene.analysis.custom.CustomAnalyzer;
  import org.apache.lucene.document.Document;
  import org.apache.lucene.document.Field.Store;
  import org.apache.lucene.document.TextField;
  import org.apache.lucene.index.IndexWriter;
  import org.apache.lucene.index.IndexWriterConfig;
  import org.apache.lucene.index.IndexWriterConfig.OpenMode;
  import org.apache.lucene.store.Directory;
  import org.apache.lucene.store.FSDirectory;
  import zemberek.core.logging.Log;
  import zemberek.normalization.TextCleaner;
  import zemberek.tokenization.TurkishTokenizer;
  
  public class LuceneIndexer {
  
    Path indexPath;
  
    public LuceneIndexer(Path indexPath) {
      this.indexPath = indexPath;
    }
  
    public void addDocs(IndexWriter writer, Path corpusFile) throws IOException {
      List<WebDocument> corpus = WebCorpus.loadDocuments(corpusFile);
      for (WebDocument d : corpus) {
        List<String> sentences = TextCleaner.cleanAndExtractSentences(d.lines);
  
        for (String sentence : sentences) {
          sentence = sentence.replaceAll("\\s+", " ");
          String tokenized = String.join(" ",
              TurkishTokenizer.DEFAULT.tokenizeToStrings(sentence));
          Document doc = new Document();
          doc.add(new TextField("content", tokenized, Store.YES));
          writer.addDocument(doc);
        }
      }
    }
  
    public void addCorpora(List<Path> corpora, double ramBufferInMb) throws IOException {
      Directory dir = FSDirectory.open(indexPath);
      Analyzer analyzer = CustomAnalyzer.builder()
          .withTokenizer("standard")
          .addTokenFilter(LuceneLemmaFilter.Factory.class)
          .build();
      IndexWriterConfig iwc = new IndexWriterConfig(analyzer);
  
      iwc.setOpenMode(OpenMode.CREATE_OR_APPEND);
  
      iwc.setRAMBufferSizeMB(ramBufferInMb);
      IndexWriter writer = new IndexWriter(dir, iwc);
  
      for (Path path : corpora) {
        Log.info("Adding %s", path);
        addDocs(writer, path);
      }
      writer.close();
    }
  
    public void addCorpora(List<Path> corpora) throws IOException {
      addCorpora(corpora, 1024);
    }
  
    public static void main(String[] args) throws IOException {
      Path indexRoot = Paths.get("/media/ahmetaa/depo/zemberek/data/corpus-index-lemma");
      LuceneIndexer index = new LuceneIndexer(indexRoot);
  
      Path corporaRoot = Paths.get("/media/ahmetaa/depo/zemberek/data/corpora/www.cnnturk.com");
      List<Path> corpora = Files.walk(corporaRoot, 1)
          .filter(s -> s.toFile().isFile())
          .collect(Collectors.toList());
      index.addCorpora(corpora, 1024 * 4);
    }
  
  }
  