code: public static void pack(File sourceDir, OutputStream os, NameMapper mapper) {
      pack(sourceDir, os, mapper, DEFAULT_COMPRESSION_LEVEL);
    }
docs: Compresses the given directory and all of its sub-directories into the passed in
  stream. It is the responsibility of the caller to close the passed in
  stream properly.
  
  @param sourceDir
  root directory.
  @param os
  output stream (will be buffered in this method).
  @param mapper
  call-back for renaming the entries.
  
  @since 1.10