code: private void setMultipart(String contentType) {
          String[] dataBoundary = HttpPostRequestDecoder.getMultipartDataBoundary(contentType);
          if (dataBoundary != null) {
              multipartDataBoundary = dataBoundary[0];
              if (dataBoundary.length > 1 && dataBoundary[1] != null) {
                  charset = Charset.forName(dataBoundary[1]);
              }
          } else {
              multipartDataBoundary = null;
          }
          currentStatus = MultiPartStatus.HEADERDELIMITER;
      }
docs: Set from the request ContentType the multipartDataBoundary and the possible charset.