//檔案下載
@WebServlet("/down")
public class DownLoadServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //0.跳過許可權檢查和積分檢查
        //1.獲取被下載的資原始檔名稱
 

        String filename = req.getParameter("fileName");
        System.out.println(filename);
        if (filename != null && "".equals(filename.trim())) {
            //對獲取到的引數進行重新編碼,因為可能會有中文亂碼的問題
            filename = new String(filename.getBytes("ISO-8859-1"), "utf-8");
            System.out.println(filename);
        }

        
        
 
//2.從伺服器中找到被下載資源的絕對路徑
        String path = req.getServletContext().getRealPath("/WEB-INF/download/" + filename);
        System.out.println(path);
        // ----------------------------------------------------------------------------------------

        //2.1告訴瀏覽器不要直接開啟檔案,而是彈出下載框,儲存檔案
        resp.setContentType("application/x-msdownload");
        
 
//2.2應該設定下載檔案的建議儲存名稱

        //---------------------------------------------------------------------------------
        String useragent = req.getHeader("User-Agent");
        //下面兩種方式谷歌瀏覽器全部都支援
        if (useragent.contains("MSIE")) {
            //filename = URLEncoder.encode(filename, "UTF-8");
            //System.out.println(filename);
            
            // IE瀏覽器的處理方式: 
            resp.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(filename, "UTF-8"));
            
            
        } else {
            //非IE瀏覽器的處理方式:
            //resp.setHeader("Content-Disposition", "attachment;filename="+(new String(filename.getBytes("utf-8"), "ISO-8859-1")));
            filename = new String(filename.getBytes("utf-8"), "ISO-8859-1");
            System.out.println(filename);
        }
        //---------------------------------------------------------------------------------

        // 3.磁碟檔案-->程式中-->響應給使用者
        Files.copy(Paths.get(path), resp.getOutputStream());
    }

}