关于下载远程文件为未知文件.txt的解决方法

本地下载文件后缀正常，服务器下载文件后缀都为.txt的解决方法：

后缀为 未知文件.txt 的原因为前端无权限获取Content-Disposition中的文件名

response.setHeader("content-type", "application/octet-stream");
response.setContentType("application/octet-stream");
//将文件名设置到 Content-Disposition
response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName,"UTF-8"));
// 这一行一定要加 意为允许前端获取Content-Disposition的文件名 
response.setHeader("Access-Control-Expose-Headers", "Content-Disposition");

下载远程文件代码：

        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>1.3.2</version>
        </dependency>

需引入commons-io使用IOUtils

此处文件路径例如：http://127.0.0.1:8085/upload/1_1612234092195.jpg

    /**
     * 流下载
     * @param request HttpServletRequest
     * @param response HttpServletResponse
     * @param filePath 文件路径
     */
public void downloadFile(HttpServletRequest request, HttpServletResponse response, String filePath) {
    OutputStream os = null; //输出流
    try {
        os = response.getOutputStream();

        //获取文件名
        String fileName = downloadFileDTO.getFilePath().substring(filePath.lastIndexOf("/")+1);

        response.setHeader("content-type", "application/octet-stream");
        response.setContentType("application/octet-stream");
  
		//将文件名设置到 Content-Disposition
        response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName,"UTF-8"));
        
        //允许前端获取Content-Disposition中的文件名
        response.setHeader("Access-Control-Expose-Headers", "Content-Disposition");

        URL url = new URL (filePath);
        URLConnection uc = url.openConnection();
        IOUtils.copy(uc.getInputStream(), os);
        os.flush();

    }catch (Exception e){
        log.error("下载文件失败:{}",e.getMessage());
    }finally {
        try {
            if(os !=null){
                os.close();
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}