在Java servlet中成功下载excel文件后，如何发出警报消息？

Question

我要在成功下载Excel文件后显示警报消息。我的程序成功下载了文件，但没有显示警告消息。

我在下面添加了Java Servlet代码部分，该部分创建和下载excel文件。您能否建议我要发出警报消息该怎么做？

        response.setContentType("application/vnd.ms-excel");
        response.setCharacterEncoding("UTF-8");
        response.setHeader("Content-Disposition", "attachment; filename=\"" + excelFileName + "\"");
        .
        .
        .     // excel creating code
        .
        .

            // Write data in the excel
            ServletOutputStream out = response.getOutputStream();
            workbook.write(out);

            // Close  workbook
            workbook.close();

            // This below code is supposed to be executed to give alert message but it doesn't work
            PrintStream pw = new PrintStream(out, true, "utf-8");
            response.setContentType("text/html");
            pw.println("<script type=\"text/javascript\">");
            pw.println("alert('" + download_success_message + "');");    
            pw.println("history.back();");
            // pw.println("location='jsp/Hus3report.jsp';");
            pw.println("</script>");

            out.flush();
            out.close();

        } catch (Exception e) {
            e.printStackTrace();
        }

    } else {
        PrintWriter pw = response.getWriter();
        response.setContentType("text/html");
        pw.println("<script type=\"text/javascript\">");
        pw.println("alert('" + no_data_available + "');");
        pw.println("history.back();");
        // pw.println("location='jsp/Hus3report.jsp';");
        pw.println("</script>");
    }