protected void doGet(HttpServletRequest request, HttpServletResponse response)
     throws ServletException, IOException {
   BookDao dao = new BookDao();
   if (request.getParameter("type") == null || request.getParameter("type").equals("全部类型")) {
     request.getSession().setAttribute("queryBooks", dao.queryBook(null, BookDao.QUERY_BY_TYPE));
   } else {
     LinkedList<Book> list = dao.queryBook(request.getParameter("type"), BookDao.QUERY_BY_TYPE);
     request.getSession().setAttribute("queryBooks", list);
   }
   request.getSession().setAttribute("who", "book");
   request.getRequestDispatcher("/back_stage.jsp").forward(request, response);
   dao.giveBack();
 }
 protected void doPost(HttpServletRequest request, HttpServletResponse response)
     throws ServletException, IOException {
   String bookname = request.getParameter("bookname");
   byte[] bytes = bookname.getBytes("ISO-8859-1");
   bookname = new String(bytes, "UTF-8");
   HttpSession session = request.getSession();
   BookDao dao = new BookDao();
   LinkedList<Book> list = new LinkedList<>();
   LinkedList<Book> sessionkList = (LinkedList<Book>) session.getAttribute("queryBooks");
   if (sessionkList != null) {
     for (Book book : sessionkList) {
       if (book.getName().contains(bookname)) {
         list.add(book);
         break;
       }
     }
   }
   session.setAttribute("queryBooks", list);
   session.setAttribute("who", "book"); // 显示书
   request.getRequestDispatcher("/back_stage.jsp").forward(request, response);
   dao.giveBack();
 }