/**
   * Load classes from given file. File could be either directory or JAR file.
   *
   * @param clsLdr Class loader to load files.
   * @param file Either directory or JAR file which contains classes or references to them.
   * @return Set of found and loaded classes or empty set if file does not exist.
   * @throws GridSpiException Thrown if given JAR file references to none existed class or
   *     IOException occurred during processing.
   */
  static Set<Class<? extends GridTask<?, ?>>> getClasses(ClassLoader clsLdr, File file)
      throws GridSpiException {
    Set<Class<? extends GridTask<?, ?>>> rsrcs = new HashSet<Class<? extends GridTask<?, ?>>>();

    if (file.exists() == false) {
      return rsrcs;
    }

    GridUriDeploymentFileResourceLoader fileRsrcLdr =
        new GridUriDeploymentFileResourceLoader(clsLdr, file);

    if (file.isDirectory()) {
      findResourcesInDirectory(fileRsrcLdr, file, rsrcs);
    } else {
      try {
        for (JarEntry entry : U.asIterable(new JarFile(file.getAbsolutePath()).entries())) {
          Class<? extends GridTask<?, ?>> rsrc = fileRsrcLdr.createResource(entry.getName(), false);

          if (rsrc != null) {
            rsrcs.add(rsrc);
          }
        }
      } catch (IOException e) {
        throw new GridSpiException(
            "Failed to discover classes in file: " + file.getAbsolutePath(), e);
      }
    }

    return rsrcs;
  }