code: private String getFilenameForKey(String key) {
          int firstHalfLength = key.length() / 2;
          String localFilename = String.valueOf(key.substring(0, firstHalfLength).hashCode());
          localFilename += String.valueOf(key.substring(firstHalfLength).hashCode());
          return localFilename;
      }
docs: Creates a pseudo-unique filename for the specified cache key.
  @param key The key to generate a file name for.
  @return A pseudo-unique filename.