错误

前端上传文件，后端方法中 @RequestParam("file") MultipartFile file 方法接收报错。

原因

刷新页面的请求地址是：http://localhost:8080/uploadImage，后台中上传文件的映射地址（action="/uploadImage"）也是 /uploadImage，刚打开上传页面 uploadImage.html 刷新时的请求并非是一个 multipart request 请求，没有 MultipartFile 等参数，故此报错。

待刷新的页面：
http://localhost:8080/uploadImage

上传的地址：

<form enctype="multipart/form-data" action="/uploadImage" method="POST">

    @RequestMapping(value = "/uploadImage" )
    public String upload(@RequestParam("file") MultipartFile file) throws Exception {
        if (file.isEmpty()){
            // TODO
        }
        return "uploadImage.html";
    }

解决方法

1. 需要添加一个获取上传页面的方法映射上传页。
2. 修改上传文件的映射地址，如 <form enctype="multipart/form-data" action="/insertImage" method="POST">

修改后

HTML：uploadImage.html

<form enctype="multipart/form-data" action="/upload" method="POST">
    <div class="form-group">
        <label>文件上传</label>
        <input type="file" name="fileName" accept="image/*">
    </div>
    <button type="submit" class="btn btn-primary">上传</button>
    &nbsp;&nbsp;&nbsp;&nbsp;
    <button type="reset" class="btn btn-secondary">重置</button>
</form>

controller：

    /**
     * @Description: 正常访问 图像上传页面
     * @Date: 2019/11/8 19:05
     * @Params:
     * @ReturnType:
     **/
    @RequestMapping(value = "/uploadImage")
    public String uploadImagePage() {
        return "/uploadImage";
    }


    /**
     * @Description: 上传图像
     * @Date: 2019/11/8 19:06
     * @Params:
     * @ReturnType:
     **/
    @RequestMapping(value = "/upload")
    @ResponseBody
    public ModelAndView upload(@RequestParam("fileName") MultipartFile file) throws Exception {
        ModelAndView modelAndView = new ModelAndView();
        String uploadRes = "";
        if (Objects.isNull(file) || file.isEmpty() || Strings.isEmpty(file.getOriginalFilename())) {
            modelAndView.setViewName("uploadImage.html");
            return modelAndView;
        }
        String fileName = file.getOriginalFilename();
        fileName = fileName.substring(fileName.lastIndexOf("\\") + 1);

        int size = (int) file.getSize();
        logger.info(String.format("文件[%s] 大小为[%s]", fileName, size));

        String rootPath = "F://test";
        try {
            // 保存文件
            File dest = new File(rootPath + "/" + fileName);
            file.transferTo(dest);
            uploadRes = "true";
        } catch (Exception e) {
            e.printStackTrace();
            uploadRes = "false";
        }
        modelAndView.addObject("uploadResult", uploadRes);
        modelAndView.setViewName("uploadImage.html");
        return modelAndView;
    }

参考链接

https://www.jianshu.com/p/be1af489551c
https://blog.csdn.net/ahwsk/article/details/79707807
https://www.cnblogs.com/luxd/p/9264826.html