为什么在使用spring上传文件时需要在配置CommonsMultipartResolver之后配置MultipartFilter？

Question

我正在开发用于文件上传的API，并且需要代理。不使用代理时，只需添加config：

<bean id="multipartResolver"
      class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
    <!-- one of the properties available; the maximum file size in bytes 400m -->
    <property name="maxUploadSize" value="419430400" />
</bean>

API将正常运行如下：

@RequestMapping(value = "/tags/build", method = RequestMethod.POST)
public Object buildTag(String repoName, String tag, @RequestParam(value = "dockerFile", required = true) MultipartFile dockerFile,
        HttpServletRequest request, HttpServletResponse response) {

但添加代理，它不起作用，代理：

@RequestMapping("/**")
@ResponseBody
public String mirror(@RequestBody(required = false) String body, HttpMethod method, HttpServletRequest request, HttpServletResponse response) throws URISyntaxException {
    ...
    try {
        restTemplate.getMessageConverters().add(0, new StringHttpMessageConverter(Charset.forName("UTF-8")));
        restTemplate.setRequestFactory(new CloudClientHttpRequestFactory(30000, 5000));
        ResponseEntity<String> responseEntity = restTemplate.exchange(uri, HttpMethod.valueOf(request.getMethod()), entity, String.class);
        String responseBody = responseEntity.getBody();

但是当我在代理web.xml中添加MultipartFilter时，它也可以工作。为什么？有什么身体可以帮助我吗？提前致谢。我用谷歌搜索，但找不到满意的答案。