@Override
          public File lookup() throws IOException {
            checkOpen(); // per the spec, must check that the stream is open for each view operation
            return view.lookUpWithLock(checkedPath, optionsSet).requireExists(checkedPath).file();
          }
A stream filter that always returns true.
jimfs/src/main/java/com/google/common/jimfs/JimfsSecureDirectoryStream.java