import org.apache.lucene.store.NoSuchDirectoryException; //导入依赖的package包/类
/**
 * Get the generation of the most recent commit to the
 * index in this directory (N in the segments_N file).
 *
 * @param directory -- directory to search for the latest segments_N file
 */
public static long getLastCommitGeneration(Directory directory) throws IOException {
  try {
    return getLastCommitGeneration(directory.listAll());
  } catch (NoSuchDirectoryException nsde) {
    return -1;
  }
}
 

import org.apache.lucene.store.NoSuchDirectoryException; //导入依赖的package包/类
/**
 * Returns <code>true</code> if an index likely exists at
 * the specified directory.  Note that if a corrupt index
 * exists, or if an index in the process of committing 
 * @param  directory the directory to check for an index
 * @return <code>true</code> if an index exists; <code>false</code> otherwise
 */
public static boolean indexExists(Directory directory) throws IOException {
  // LUCENE-2812, LUCENE-2727, LUCENE-4738: this logic will
  // return true in cases that should arguably be false,
  // such as only IW.prepareCommit has been called, or a
  // corrupt first commit, but it's too deadly to make
  // this logic "smarter" and risk accidentally returning
  // false due to various cases like file description
  // exhaustion, access denied, etc., because in that
  // case IndexWriter may delete the entire index.  It's
  // safer to err towards "index exists" than try to be
  // smart about detecting not-yet-fully-committed or
  // corrupt indices.  This means that IndexWriter will
  // throw an exception on such indices and the app must
  // resolve the situation manually:
  String[] files;
  try {
    files = directory.listAll();
  } catch (NoSuchDirectoryException nsde) {
    // Directory does not exist --> no index exists
    return false;
  }

  // Defensive: maybe a Directory impl returns null
  // instead of throwing NoSuchDirectoryException:
  if (files != null) {
    String prefix = IndexFileNames.SEGMENTS + "_";
    for(String file : files) {
      if (file.startsWith(prefix) || file.equals(IndexFileNames.SEGMENTS_GEN)) {
        return true;
      }
    }
  }
  return false;
}
 

import org.apache.lucene.store.NoSuchDirectoryException; //导入依赖的package包/类
public void testNoDir() throws Throwable {
  File tempDir = createTempDir("doesnotexist");
  TestUtil.rm(tempDir);
  Directory dir = newFSDirectory(tempDir);
  try {
    DirectoryReader.open(dir);
    fail("did not hit expected exception");
  } catch (NoSuchDirectoryException nsde) {
    // expected
  }
  dir.close();
}
 

import org.apache.lucene.store.NoSuchDirectoryException; //导入依赖的package包/类
public void testNoDir() throws Throwable {
  File tempDir = _TestUtil.getTempDir("doesnotexist");
  _TestUtil.rmDir(tempDir);
  Directory dir = newFSDirectory(tempDir);
  try {
    DirectoryReader.open(dir);
    fail("did not hit expected exception");
  } catch (NoSuchDirectoryException nsde) {
    // expected
  }
  dir.close();
}
 

import org.apache.lucene.store.NoSuchDirectoryException; //导入依赖的package包/类
public boolean isEmpty() throws IOException {
	rwl.r.lock();
	try {
		return ArrayUtils.isEmpty(directory.listAll());
	} catch (NoSuchDirectoryException e) {
		return true;
	} finally {
		rwl.r.unlock();
	}
}