帮忙看一下为什么修改不了数据库信息

Question

Servlet代码@WebServlet("/UpdateStudent") public class UpdateStudent extends HttpServlet {     private static final long serialVersionUID = 1L;     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {         String idStr = request.getParameter("id");         if(idStr != null && !idStr.equals("")){             int id = Integer.valueOf(idStr);             AdminDao dao = new AdminDao();             Student stu = dao.selectStudentById(id);             request.setAttribute("stu", stu);         }         request.getRequestDispatcher("/UpdateStudent.jsp").forward(request, response);     }     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {         String sname = request.getParameter("sname");         String password = request.getParameter("password");         String sno = request.getParameter("sno");         String sex = request.getParameter("sex");         String major = request.getParameter("major");         String grade = request.getParameter("grade");         Student student = new Student();         student.setSname(new String(sname.getBytes("ISO-8859-1"),"UTF-8"));         student.setPassword(password);         student.setSno(sno);         student.setSex(new String(sex.getBytes("ISO-8859-1"),"UTF-8"));         student.setMajor(new String(major.getBytes("ISO-8859-1"),"UTF-8"));         student.setGrade(new String(grade.getBytes("ISO-8859-1"),"UTF-8"));         AdminDao dao = new AdminDao();         dao.UpdateStudent(student);         request.getRequestDispatcher("/Information").forward(request, response); }

Answer 1

e.printStackTrace();
看看有没有输出什么错误

在DAO代码加上日志输出，看看它本身有没有执行

再输出下传进来的Student stu参数看下，修改的stu对象的各个字段是什么

Answer 2

cmd.setInt(1, stu.getId());应该改为cmd.setInt(7, stu.getId());就对了，注意sql语句注入顺序