Question

我正在开发一个Web应用程序（Java / JSP），其中一部分是允许用户仅下载所请求的文件＆＃34;一次＆＃34;。当他们遇到＆＃34;下载＆＃34;按钮，他们将被要求保存/打开或取消该文件，他们回应的文件将被标记为已下载，用户无法再次下载。我尝试找出一种方法，当用户用＆＃34;取消＆＃34;并检查用户是否真的完全下载了该文件。

这是Java部分：

@WebServlet("/download")
    public class download extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private static final int DEFAULT_BUFFER_SIZE = 10240;
/**
 * @see HttpServlet#HttpServlet()
 */
public download() {
    super();
    // TODO Auto-generated constructor stub
}

/**
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
 *      response)
 */
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    try {

        Class.forName("org.sqlite.JDBC");
        Connection c = DriverManager.getConnection("jdbc:sqlite:C:\\sqlite\\mascapp.db");
        c.setAutoCommit(false);
        Cookie[] cookies = request.getCookies();
        if(request.getSession().getAttribute("aeid") == null || request.getSession().getAttribute("uid") == null)
        {
            response.sendRedirect("/index.jsp");
        }
        int ae_num = Integer.parseInt(request.getSession().getAttribute("aeid").toString());




        String sql = "SELECT file, filename FROM reports INNER JOIN download USING(tipid) WHERE reports.tipid = ?"+
                "AND download.ts_" + ae_num+ " = 0;";

        PreparedStatement stmt = c.prepareStatement(sql);
        String tipNum = request.getParameter("tipid");
        if (tipNum != null) {

            stmt.setString(1, tipNum);
            //stmt.setString(2, tipNum);
            ResultSet res = stmt.executeQuery();
            BufferedInputStream fileBlob = null;
            String filename = "";

            while (res.next()) {
                fileBlob = new BufferedInputStream(res.getBinaryStream("file"), DEFAULT_BUFFER_SIZE);

                filename = res.getString("filename");
            }
            if (fileBlob != null) {
                System.out.println(filename);
                response.setContentType("APPLICATION/OCTET-STREAM");
                response.setHeader("Content-Disposition", "attachment; filename=\"" + filename + "\"");

                BufferedOutputStream output = new BufferedOutputStream(response.getOutputStream(),
                        DEFAULT_BUFFER_SIZE);

                byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
                int length;
                while ((length = fileBlob.read(buffer)) > 0) {
                    output.write(buffer, 0, length);
                }

                output.close();
                fileBlob.close();
                Date now = new Date();

                sql = "UPDATE download SET ts_" + ae_num + " = " + now.getTime() + " WHERE tipid = ?;";
                System.out.println(sql);
                stmt = c.prepareStatement(sql);
                stmt.setString(1, tipNum);

                stmt.executeUpdate();
                stmt.close();

                c.commit();
                c.close();
            }
            else
            {

                c.close();
                response.sendRedirect("/MASC/formdownloaded.jsp");

            }
        }
        else
        {
            response.getWriter().append("<html><body><h1>Error: no param</h1></body></html>");
            c.close();

        }
    } catch (SQLException | ClassNotFoundException e) {
        e.printStackTrace();

    }
}

/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
 *      response)
 */
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    // TODO Auto-generated method stub
    doGet(request, response);
}

}

任何解决方案或建议？！提前谢谢。

Answer 1

答案是不要那样做。那些对话是有充分理由的，其中一些涉及安全。

您想要做的事情取决于为什么您只希望用户下载文件一次。下载可能由于各种原因而失败，那么如果用户在下载过程中失去连接，您会怎么做？

Answer 2

检查此页面：http://johnculviner.com/jquery-file-download-plugin-for-ajax-like-feature-rich-file-downloads/（此链接有时无效，如果您遇到问题，请链接到github：https://github.com/johnculviner/jquery.fileDownload）。

看起来你可以做的最好的事情是确保通过检查从服务器发回的客户端特殊cookie并下载文件流来启动下载。为此，你必须像这个线程一样将Cookie添加到servlet响应中： Set cookie only after file download complete.

因此，在servlet中的doGet方法结束时，你应该有类似的东西：

Cookie fileDwnld = new Cookie("fileDownload", "true");
fileDwnld.setPath("/");
response.addCookie(fileDwnld);

这是客户端代码：

<script src="http://code.jquery.com/jquery-2.1.4.min.js"></script>
<script src="jquery.fileDownload.js"></script>
<script>
$(document).ready(function() {
    $("#btnSubmit").click(function(){
        $.fileDownload('path/to/servlet')
            .done(function () { alert('File download a success!'); })
            .fail(function () { alert('File download failed!'); });
    }); 
});

Answer 3

我没有正确的答案，但我确实知道“附件”;如果你理解我的意思，在标题中强制浏览器“下载”文件，与“打开它”相比。尝试删除该标题，看看你是否获得了预期的效果。

使用Java检测并报告已完成的下载

3 个答案: