code: @Override
      public void handleRequest(final HttpServerExchange exchange) throws Exception {
          // parse the body to map or list if content type is application/json
          String contentType = exchange.getRequestHeaders().getFirst(Headers.CONTENT_TYPE);
          if (contentType != null) {
              if (exchange.isInIoThread()) {
                  exchange.dispatch(this);
                  return;
              }
              exchange.startBlocking();
              try {
                  if (contentType.startsWith("application/json")) {
                      InputStream inputStream = exchange.getInputStream();
                      String unparsedRequestBody = StringUtils.inputStreamToString(inputStream, StandardCharsets.UTF_8);
                      // attach the unparsed request body into exchange if the cacheRequestBody is enabled in body.yml
                      if (config.isCacheRequestBody()) {
                          exchange.putAttachment(REQUEST_BODY_STRING, unparsedRequestBody);
                      }
                      // attach the parsed request body into exchange if the body parser is enabled
                      attachJsonBody(exchange, unparsedRequestBody);
                  } else if (contentType.startsWith("multipart/form-data") || contentType.startsWith("application/x-www-form-urlencoded")) {
                      // attach the parsed request body into exchange if the body parser is enabled
                      attachFormDataBody(exchange);
                  }
              } catch (IOException e) {
                  logger.error("IOException: ", e);
                  setExchangeStatus(exchange, CONTENT_TYPE_MISMATCH, contentType);
                  return;
              }
          }
          Handler.next(exchange, next);
      }
docs: Check the header starts with application/json and parse it into map or list
  based on the first character "{" or "[". Otherwise, check the header starts
  with application/x-www-form-urlencoded or multipart/form-data and parse it
  into formdata
  
  @param exchange HttpServerExchange
  @throws Exception Exception