lucene4.7源码研究之索引建立过程(1)

Directory directory = FSDirectory.open(file);

/** Creates an FSDirectory instance, trying to pick the
   *  best implementation given the current environment.
   *  The directory returned uses the {@link NativeFSLockFactory}.
   *
   *  
Currently this returns {@link MMapDirectory} for most Solaris
   *  and Windows 64-bit JREs, {@link NIOFSDirectory} for other
   *  non-Windows JREs, and {@link SimpleFSDirectory} for other
   *  JREs on Windows. It is highly recommended that you consult the
   *  implementation‘s documentation for your platform before
   *  using this method.
   *
   * 
NOTE: this method may suddenly change which
   * implementation is returned from release to release, in
   * the event that higher performance defaults become
   * possible; if the precise implementation is important to
   * your application, please instantiate it directly,
   * instead. For optimal performance you should consider using
   * {@link MMapDirectory} on 64 bit JVMs.
   *
   * 
See above */
  public static FSDirectory open(File path) throws IOException {
    return open(path, null);//使用默认锁工厂
  }

  /** Just like {@link #open(File)}, but allows you to
   *  also specify a custom {@link LockFactory}. */
  public static FSDirectory open(File path, LockFactory lockFactory) throws IOException {
    if ((Constants.WINDOWS || Constants.SUN_OS || Constants.LINUX)
          && Constants.JRE_IS_64BIT && MMapDirectory.UNMAP_SUPPORTED) {
      return new MMapDirectory(path, lockFactory);
    } else if (Constants.WINDOWS) {
      return new SimpleFSDirectory(path, lockFactory);
    } else {
      return new NIOFSDirectory(path, lockFactory);
    }
  }

  /** Create a new NIOFSDirectory for the named location.
   * 
   * @param path the path of the directory
   * @param lockFactory the lock factory to use, or null for the default
   * ({@link NativeFSLockFactory});
   * @throws IOException if there is a low-level I/O error
   */
  public NIOFSDirectory(File path, LockFactory lockFactory) throws IOException {
    super(path, lockFactory);
  }

/** Create a new FSDirectory for the named location (ctor for subclasses).
   * @param path the path of the directory
   * @param lockFactory the lock factory to use, or null for the default
   * ({@link NativeFSLockFactory});
   * @throws IOException if there is a low-level I/O error
   */
  protected FSDirectory(File path, LockFactory lockFactory) throws IOException {
    // new ctors use always NativeFSLockFactory as default:
    if (lockFactory == null) {
      lockFactory = new NativeFSLockFactory();
    }
    directory = getCanonicalPath(path);//获取path绝对路径

    if (directory.exists() && !directory.isDirectory())
      throw new NoSuchDirectoryException("file ‘" + directory + "‘ exists but is not a directory");

    setLockFactory(lockFactory);//设置锁工厂

  }

  /**
   * Create a NativeFSLockFactory instance, with null (unset)
   * lock directory. When you pass this factory to a {@link FSDirectory}
   * subclass, the lock directory is automatically set to the
   * directory itself. Be sure to create one instance for each directory
   * your create!
   */
  public NativeFSLockFactory() {
    this((File) null);//工厂没有设置路径
  }

@Override
  public void setLockFactory(LockFactory lockFactory) throws IOException {
    super.setLockFactory(lockFactory);

    // for filesystem based LockFactory, delete the lockPrefix, if the locks are placed
    // in index dir. If no index dir is given, set ourselves
    if (lockFactory instanceof FSLockFactory) {
      final FSLockFactory lf = (FSLockFactory) lockFactory;
      final File dir = lf.getLockDir();//因为（File）null，所以dir为null
      // if the lock factory has no lockDir set, use the this directory as lockDir
      if (dir == null) {
        lf.setLockDir(directory);//使用我们设置的directory
        lf.setLockPrefix(null);
      } else if (dir.getCanonicalPath().equals(directory.getCanonicalPath())) {
        lf.setLockPrefix(null);
      }
    }

  }

@Override
  public String toString() {
    return getClass().getSimpleName() + ‘@‘ + Integer.toHexString(hashCode()) + " lockFactory=" + getLockFactory();
  }