SpringBoot返回文件使前端下载的几种方式小结

    @GetMapping("/file/download")
    public void fileDownload(HttpServletResponse response, @RequestParam("filePath") String filePath) {
        File file = new File(filePath);
        if (!file.exists()) {
            throw new BusinessException("当前下载的文件不存在，请检查路径是否正确");
        }

        // 将文件写入输入流
        try (InputStream is = new BufferedInputStream(Files.newInputStream(file.toPath()))) {
            
            // 一次性读取到内存中
            byte[] buffer = new byte[is.available()];
            int read = is.read(buffer);

            // 清空 response
            response.reset();
            response.setCharacterEncoding("UTF-8");

            // Content-Disposition的作用：告知浏览器以何种方式显示响应返回的文件，用浏览器打开还是以附件的形式下载到本地保存
            // attachment表示以附件方式下载   inline表示在线打开   "Content-Disposition: inline; filename=文件名.mp3"
            // filename表示文件的默认名称，因为网络传输只支持URL编码的相关支付，因此需要将文件名URL编码后进行传输,前端收到后需要反编码才能获取到真正的名称
            response.addHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(file.getName(), "UTF-8"));

            // 告知浏览器文件的大小
            response.addHeader("Content-Length", "" + file.length());

            OutputStream outputStream = new BufferedOutputStream(response.getOutputStream());
            response.setContentType("application/octet-stream");
            outputStream.write(buffer);
            outputStream.flush();
            outputStream.close();

        } catch (IOException e) {
            throw new RuntimeException(e);
        }

    }

    @GetMapping("/file/download")
    public void fileDownload(HttpServletResponse response, @RequestParam("filePath") String filePath) {
        File file = new File(filePath);
        if (!file.exists()) {
            throw new BusinessException("当前下载的文件不存在，请检查路径是否正确");
        }

        // 清空 response
        response.reset();
        response.setCharacterEncoding("UTF-8");

        response.addHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(file.getName(), "UTF-8"));
        response.setContentType("application/octet-stream");

        // 将文件读到输入流中
        try (InputStream is = new BufferedInputStream(Files.newInputStream(file.toPath()))) {
            
            OutputStream outputStream = new BufferedOutputStream(response.getOutputStream());
            
            byte[] buffer = new byte[1024];
            int len;

            //从输入流中读取一定数量的字节，并将其存储在缓冲区字节数组中，读到末尾返回-1
            while((len = is.read(buffer)) > 0){
                outputStream.write(buffer, 0, len);
            }

            outputStream.close();

        } catch (IOException e) {
            throw new RuntimeException(e);
        }

    }

    @GetMapping("/net/download")
    public void netDownload(HttpServletResponse response, @RequestParam("fileAddress") String fileAddress, @RequestParam("filename") String filename) {

        try {
            URL url = new URL(fileAddress);
            URLConnection conn = url.openConnection();
            InputStream inputStream = conn.getInputStream();

            response.reset();
            response.setContentType(conn.getContentType());

            response.setHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(filename, "UTF-8"));

            byte[] buffer = new byte[1024];
            int len;
            
            OutputStream outputStream = response.getOutputStream();
            
            while ((len = inputStream.read(buffer)) > 0) {
                outputStream.write(buffer, 0, len);
            }
            
            inputStream.close();
            
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        
    }

    @GetMapping("/netDownloadLocal")
    public void downloadNet(@RequestParam("netAddress") String netAddress, @RequestParam("filepath") String filepath) {

        try {
            URL url = new URL(netAddress);
            URLConnection conn = url.openConnection();
            InputStream inputStream = conn.getInputStream();

            FileOutputStream fileOutputStream = new FileOutputStream(filepath);
            int byteread;
            byte[] buffer = new byte[1024];

            while ((byteread = inputStream.read(buffer)) != -1) {
                fileOutputStream.write(buffer, 0, byteread);
            }

            fileOutputStream.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }

    }