String content = "fruit=apple&vegetable=kale";
this.servletRequest.setContent(content.getBytes("UTF-8"));
this.servletRequest.setContentType(MediaType.APPLICATION_FORM_URLENCODED_VALUE);
List<HttpMessageConverter<?>> converters = new ArrayList<HttpMessageConverter<?>>();
converters.add(new AllEncompassingFormHttpMessageConverter());
RequestResponseBodyMethodProcessor processor = new RequestResponseBodyMethodProcessor(converters);
@SuppressWarnings("unchecked")
MultiValueMap<String, String> result = (MultiValueMap<String, String>) processor.resolveArgument(
paramMultiValueMap, mavContainer, webRequest, binderFactory);