public IndexMerger() 
{

}

 public IndexMerger(Configuration conf) 
{
    setConf(conf);
}

 public static  void main(String[] args) throws Exception 
{
    int res = ToolRunner.run(NutchConfiguration.create(), new IndexMerger(), args);
    System.exit(res);
}

Create an index for the input files in the named directory.

 public  void merge(Path[] indexes,
    Path outputIndex,
    Path localWorkingDir) throws IOException 
{
    LOG.info("merging indexes to: " + outputIndex);
    FileSystem localFs = FileSystem.getLocal(getConf());  
    if (localFs.exists(localWorkingDir)) {
      localFs.delete(localWorkingDir, true);
    }
    localFs.mkdirs(localWorkingDir);
    // Get local output target
    //
    FileSystem fs = FileSystem.get(getConf());
    if (fs.exists(outputIndex)) {
      throw new FileAlreadyExistsException("Output directory " + outputIndex + " already exists!");
    }
    Path tmpLocalOutput = new Path(localWorkingDir, "merge-output");
    Path localOutput = fs.startLocalOutput(outputIndex, tmpLocalOutput);
    Directory[] dirs = new Directory[indexes.length];
    for (int i = 0; i <  indexes.length; i++) {
      if (LOG.isInfoEnabled()) { LOG.info("Adding " + indexes[i]); }
      dirs[i] = new FsDirectory(fs, indexes[i], false, getConf());
    }
    //
    // Merge indices
    //
    IndexWriter writer = new IndexWriter(localOutput.toString(), null, true);
    writer.setMergeFactor(getConf().getInt("indexer.mergeFactor", IndexWriter.DEFAULT_MERGE_FACTOR));
    writer.setMaxBufferedDocs(getConf().getInt("indexer.minMergeDocs", IndexWriter.DEFAULT_MAX_BUFFERED_DOCS));
    writer.setMaxMergeDocs(getConf().getInt("indexer.maxMergeDocs", IndexWriter.DEFAULT_MAX_MERGE_DOCS));
    writer.setTermIndexInterval(getConf().getInt("indexer.termIndexInterval", IndexWriter.DEFAULT_TERM_INDEX_INTERVAL));
    writer.setInfoStream(LogUtil.getDebugStream(LOG));
    writer.setUseCompoundFile(false);
    writer.setSimilarity(new NutchSimilarity());
    writer.addIndexes(dirs);
    writer.close();
    //
    // Put target back
    //
    fs.completeLocalOutput(outputIndex, tmpLocalOutput);
    LOG.info("done merging");
}

Merge all input indexes to the single output index

 public int run(String[] args) throws Exception 
{
    String usage = "IndexMerger [-workingdir < workingdir >] outputIndex indexesDir...";
    if (args.length <  2) {
      System.err.println("Usage: " + usage);
      return -1;
    }
    //
    // Parse args, read all index directories to be processed
    //
    FileSystem fs = FileSystem.get(getConf());
    List< Path > indexDirs = new ArrayList< Path >();
    Path workDir = new Path("indexmerger-" + System.currentTimeMillis());  
    int i = 0;
    if ("-workingdir".equals(args[i])) {
      i++;
      workDir = new Path(args[i++], "indexmerger-" + System.currentTimeMillis());
    }
    Path outputIndex = new Path(args[i++]);
    for (; i <  args.length; i++) {
      FileStatus[] fstats = fs.listStatus(new Path(args[i]), HadoopFSUtil.getPassDirectoriesFilter(fs));
      indexDirs.addAll(Arrays.asList(HadoopFSUtil.getPaths(fstats)));
    }
    //
    // Merge the indices
    //
    Path[] indexFiles = (Path[])indexDirs.toArray(new Path[indexDirs.size()]);
    try {
      merge(indexFiles, outputIndex, workDir);
      return 0;
    } catch (Exception e) {
      LOG.fatal("IndexMerger: " + StringUtils.stringifyException(e));
      return -1;
    } finally {
      FileSystem.getLocal(getConf()).delete(workDir, true);
    }
}