如果你按网上说的方法设置了跨域，但仍然出现这个问题，再看看你的请求头是否有如下图的属性，如果没有，那在后端直接设置一下

直接在用到的地方设置 response.setHeader("Access-Control-Allow-Origin", "*");

@PostMapping("/download/homework")
    public void hwDownload(@RequestBody Map map,HttpServletResponse response) throws Exception {
        String fileName = (String)map.get("fileName");
        FileInputStream fis = null;
        try {
            fis = new FileInputStream(LoadUtil.homeworkFolder + File.separator + fileName);
            // 清空输出流
            response.reset();
            response.setContentType("application/x-download;charset=UTF-8");
            response.setCharacterEncoding("UTF-8");
            response.setHeader("Content-Disposition", "attachment;filename=" + new String(fileName.getBytes("utf-8")));
            response.setHeader("Content-Length", String.valueOf(fis.getChannel().size()));
            response.setHeader("Access-Control-Allow-Origin", "*");

            byte[] b = new byte[100];
            int len;
            while ((len = fis.read(b)) != -1) {
                response.getOutputStream().write(b, 0, len);
            }
        } catch (IOException e) {
            logger.error("异常：" + e);
        }
        //文件的关闭放在finally中
        finally {
            try {
                response.getOutputStream().flush();
                response.getOutputStream().close();
                fis.close();
            } catch (IOException e) {
                logger.error("异常：" + e);
            }
        }
    }