Spring POST multipart/form-data，请求部分始终为空

Question

我有一个简单的 REST controller 用于接受从 HTML 表单上传的文件。 The project is Spring Boot 2.6.1 and Java 17. But the problem was also to be found in Spring Boot 2.3.7 and Java 15.

@PostMapping(path = "/file", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public void handleFileUpload(@RequestParam("file") MultipartFile file) {
    fileService.upload(file.getInputStream(), file.getOriginalFilename());
}

问题是file总是 NULL。 我发现了很多关于设置MultipartResolver bean 或启用spring.http.multipart.enabled = true的不同答案，但没有任何帮助。 我有一个日志过滤器作为链中的第一个过滤器。 在过滤器链中调试后，我发现调用request.getParts()可以使一切正常。 我的过滤器如下所示：

public class LoggingFilter extends GenericFilterBean {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
        BufferedRequestWrapper bufferedRequest = new BufferedRequestWrapper(httpServletRequest);
        BufferedResponseWrapper bufferedResponse = new BufferedResponseWrapper((HttpServletResponse) response);

        filterChain.doFilter(bufferedRequest, bufferedResponse);

        logRequest(httpServletRequest, bufferedRequest);
        logResponse(httpServletRequest, bufferedResponse);
    }

我将过滤器更改为：

public class LoggingFilter extends GenericFilterBean {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest httpServletRequest = (HttpServletRequest) request;

        if (request.getContentType() != null && request.getContentType().startsWith("multipart/form-data")) {
            httpServletRequest.getParts(); // Trigger initialization of multi-part.
        }

        BufferedRequestWrapper bufferedRequest = new BufferedRequestWrapper(httpServletRequest);
        BufferedResponseWrapper bufferedResponse = new BufferedResponseWrapper((HttpServletResponse) response);

        filterChain.doFilter(bufferedRequest, bufferedResponse);

        logRequest(httpServletRequest, bufferedRequest);
        logResponse(httpServletRequest, bufferedResponse);
    }

一切正常。 我的问题是； 为什么需要这个？ 有没有更好的方法来做到这一点？

Answer 1

请考虑使用 ContentCachingRequestWrapper。

它内置了 spring，可帮助您读取缓存从输入 stream 和阅读器读取的所有内容。

请注意，对于多部分文件，spring 已经有一个包装器... MultipartHttpServletRequest

请参考： https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/util/ContentCachingRequestWrapper.ZFC35FDC70D2882C7A7A