如何在Java Servlet中跟踪文件下载事件

Question

我有这种方法，我需要知道用户何时结束下载文件。但是在方法结束时，它会打印到控制台“结束”消息，但下载仍在运行。如何跟踪下载活动结束？

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("GET");

    response.setContentType("application/zip");
    response.setHeader("Content-disposition", "attachment; filename=abc.zip");

    File[] files = ...//getting files here

    FileOutputStream fos = new FileOutputStream("ABC.zip");
    ZipOutputStream zipOut = new ZipOutputStream(fos);
    zipOut.setLevel(0);
    for (File fileToZip : files) {
        FileInputStream fis = new FileInputStream(fileToZip);
        ZipEntry zipEntry = new ZipEntry(fileToZip.getName());
        zipOut.putNextEntry(zipEntry);

        byte[] bytes = new byte[1024];
        int length;
        while ((length = fis.read(bytes)) >= 0) {
            zipOut.write(bytes, 0, length);
        }
        fis.close();
    }
    zipOut.close();

    fos.close();

    File my_file = new File("ABC.zip");

    OutputStream out = response.getOutputStream();
    FileInputStream in = new FileInputStream(my_file);
    byte[] buffer = new byte[4096];
    int length;
    while ((length = in.read(buffer)) > 0) {
        out.write(buffer, 0, length);
    }
    in.close();
    System.out.print("file download start");
    out.flush();
    System.out.println("file download end");

}