code: public void startPart(String contentType) throws IOException {
          if (inPart)
              out.write(__CRLF);
          out.write(__DASHDASH);
          out.write(boundary);
          out.write(__CRLF);
          out.write("Content-Type: ");
          out.write(contentType);
          out.write(__CRLF);
          out.write(__CRLF);
          inPart = true;
      }
docs: Start creation of the next Content.
  
  @param contentType the content type
  @throws IOException if unable to write the part