JavaWeb实现简单文件下载

文件下载主要使用HttpServletResponse这个对象，只需要得到一个文件流，然后将这个文件流写入HttpServletResponse的输出流即可。
关键代码：

     @GetMapping("/download")
    public void fileDownload(@RequestParam("fileName") String fileName,HttpServletResponse response){
        InputStream in;
        BufferedInputStream bis;
        ServletOutputStream outputStream = null;
        try {
            //D:\\upload/a.jpg
            in=new FileInputStream(uploadPath+File.separator+fileName);
            bis=new BufferedInputStream(in);
            response.setHeader("content-type","application/force-download");
            response.setHeader("Content-Disposition","attachment;filename="+fileName);
             outputStream = response.getOutputStream();

            byte[] buffer=new byte[1024];
            int len=0;
            while((len=in.read(buffer))!=-1){
                outputStream.write(buffer,0,len);
            }
            outputStream.flush();
            outputStream.close();
            in.close();
            System.out.println("下载成功");

        } catch (FileNotFoundException e) {
            System.out.println("文件未找到");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

只需要将文件输入流，写入到HttpServletResponse的输出流中，即可，响应到前端浏览器，浏览器将会以附件的形式打开此文件—也就是下载。