code: @Override
      public Object convertRequest(ServiceRequestContext ctx, AggregatedHttpMessage request,
                                   Class<?> expectedResultType) throws Exception {
          if (expectedResultType == String.class ||
              expectedResultType == CharSequence.class) {
              final MediaType contentType = request.contentType();
              if (contentType != null && contentType.is(MediaType.ANY_TEXT_TYPE)) {
                  return request.content(
                          contentType.charset().orElse(ArmeriaHttpUtil.HTTP_DEFAULT_CONTENT_CHARSET));
              }
          }
          return RequestConverterFunction.fallthrough();
      }
docs: Converts the specified {@link AggregatedHttpMessage} to a {@link String}.