code: private void enforceCorrectEncodingOfRequest() {
  
          String charset = NinjaConstant.UTF_8;
  
          String contentType = getHeader(CONTENT_TYPE);
  
          if (contentType != null) {
              charset = HttpHeaderUtils.getCharsetOfContentTypeOrUtf8(contentType);
          }
  
          try {
              httpServletRequest.setCharacterEncoding(charset);
          } catch (UnsupportedEncodingException e) {
              logger.error("Server does not support charset of content type: " + contentType);
          }
  
      }
docs: When a servlet engine gets a content type like: "application/json" it
  assumes a default encoding of iso-xxxxx.
  
  That is not what Ninja does (and is not consistent with default encodings
  of application/json and application/xml).
  
  Therefore we'll set utf-8 as request encoding if it is not set.