1、M转F
File file = new File(path);
FileUtils.copyInputStreamToFile(multipartFile.getInputStream(), file);
2、F转M
File file = new File("src/test/resources/input.txt");
FileInputStream input = new FileInputStream(file);
MultipartFile multipartFile = new MockMultipartFile("file", file.getName(), "text/plain", IOUtils.toByteArray(input));
转自:https://www.cnblogs.com/zxg-blog/p/8952255.html