public static long getDU(File dir) {
    long size = 0;
    if (!dir.exists())
      return 0;
    if (!dir.isDirectory()) {
      return dir.length();
    } else {
      File[] allFiles = dir.listFiles();
      if (allFiles != null) {
        for (File f : allFiles) {
          if (!org.apache.commons.io.FileUtils.isSymlink(f)) {
            size += getDU(f);
          }
        }
      }
      return size;
    }
  }
@Test (timeout = 30000)
  public void testGetDU() throws Exception {
    long du = FileUtil.getDU(testFolder.getRoot());
    // Only two files (in partitioned).  Each has 3 characters + system-specific
    // line separator.
    final long expected = 2 * (3 + System.getProperty("line.separator").length());
    Assert.assertEquals(expected, du);
    
    // target file does not exist:
    final File doesNotExist = new File(tmp, "QuickBrownFoxJumpsOverTheLazyDog");
    long duDoesNotExist = FileUtil.getDU(doesNotExist);
    assertEquals(0, duDoesNotExist);
    
    // target file is not a directory:
    File notADirectory = new File(partitioned, "part-r-00000");
    long duNotADirectoryActual = FileUtil.getDU(notADirectory);
    long duNotADirectoryExpected = 3 + System.getProperty("line.separator").length();
    assertEquals(duNotADirectoryExpected, duNotADirectoryActual);
    
    try {
      // one of target files is not accessible, but the containing directory
      // is accessible:
      try {
        FileUtil.chmod(notADirectory.getAbsolutePath(), "0000");
      } catch (InterruptedException ie) {
        // should never happen since that method never throws InterruptedException.      
        assertNull(ie);  
      }
      assertFalse(FileUtil.canRead(notADirectory));
      final long du3 = FileUtil.getDU(partitioned);
      assertEquals(expected, du3);

      // some target files and containing directory are not accessible:
      try {
        FileUtil.chmod(partitioned.getAbsolutePath(), "0000");
      } catch (InterruptedException ie) {
        // should never happen since that method never throws InterruptedException.      
        assertNull(ie);  
      }
      assertFalse(FileUtil.canRead(partitioned));
      final long du4 = FileUtil.getDU(partitioned);
      assertEquals(0, du4);
    } finally {
      // Restore the permissions so that we can delete the folder 
      // in @After method:
      FileUtil.chmod(partitioned.getAbsolutePath(), "0777", true/*recursive*/);
    }
  }