// 读取文件
File file = new File("path/to/your/file.txt"); // 文件路径
FileInputStream fis = new FileInputStream(file);

// 将文件流返回给前端
response.setContentType("application/octet-stream");
response.setHeader("Content-Disposition", "attachment; filename=\"" + file.getName() + "\"");

OutputStream outputStreams = response.getOutputStream();
byte[] buffer = new byte[1024];
int len;
while ((len = fis.read(buffer)) != -1) {
    outputStreams.write(buffer, 0, len);
}
outputStreams .flush();

fis.close();
outputStreams.close();