code: public final long add(String pid, InputStream content)
              throws LowlevelStorageException {
          String filePath;
          File file = null;
          //check that object is not already in store
          if (pathRegistry.exists(pid)){
              throw new ObjectAlreadyInLowlevelStorageException(pid);
          }
  
          filePath = pathAlgorithm.get(pid);
          if (filePath == null || filePath.equals("")) { //guard against algorithm implementation
              throw new LowlevelStorageException(true,
                      "null path from algorithm for pid " + pid);
          }
  
          try {
              file = new File(filePath);
          } catch (Exception eFile) { //purposefully general catch-all
              throw new LowlevelStorageException(true,
                      "couldn't make File for " + filePath, eFile);
          }
          fileSystem.write(file, content);
          pathRegistry.put(pid, filePath);
          return file.length();
      }
docs: add to lowlevel store content of Fedora object not already in
  lowlevel store
  @return size - size of the object stored