更新jsp

Question

我正在尝试更新数据库中的数据，我有一个控制器servlet，DBhelper，User类和update.jsp。

这是控制器servlet ..

import java.io.IOException;
import java.sql.SQLException;
import java.util.List;
import javax.annotation.Resource;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
import model.DBhelper;
import user.User;


/**
 * Servlet implementation class servletJsp
 */
@WebServlet("/controller")
public class Controller extends HttpServlet {
    private static final long serialVersionUID = 1L;

    @Resource(name="")
    private DataSource dataSource;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String page;
        if(request.getParameterMap().containsKey("page")){
            page =request.getParameter("page");
        }else{
            page="index";
        }
        switch (page) {
        case "index":
            homepage(request,response);
            break;
        case "update":
            String username = request.getParameter("username"); 
            update(username, request,response);
            break;
        }   
    }

    private void update(String username, HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        if(request.getParameterMap().containsKey("action")){
            if(request.getParameter("action").equals("submit")){

                String authority = request.getParameter("authority");
                User temp = new User(username,authority);
                try {
                    new DBhelper().update(temp,dataSource);
                } catch (SQLException e) {

                    e.printStackTrace();
                }
                request.setAttribute("message", "Record updated");
                request.getRequestDispatcher("message.jsp").forward(request, response);
            }
        }else{

            User user = null;

            try {
                user = new DBhelper().getUser(username,dataSource);
            } catch (SQLException e) {

                e.printStackTrace();
            }
           //set the attribute
           request.setAttribute("user", user);
           request.getRequestDispatcher("update.jsp").forward(request, response);
        }

        }

这是DBhelper ..

    public class DBhelper {

        private ResultSet users =null;

        public List<User> getUsers(DataSource dataSource) throws SQLException {

            Connection con=null;
            Statement st= null;
            List<User> userList = new ArrayList<>();

            try{
            con =dataSource.getConnection();
            st=con.createStatement();
            String query="select * from authorities";
            users= st.executeQuery(query);
            while(users.next()){
                String authority = users.getString("Authority");
                String username = users.getString("Username");
                User temp = new User(username, authority);
                userList.add(temp);
            }
            }catch(Exception e){

                e.printStackTrace();
                return userList;

            }finally{
                con.close();
                st.close();
            }
            return userList;
        }



    public User getUser(String username, DataSource dataSource) throws SQLException {
        Connection conn = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        User user =null;
        try{

        conn = dataSource.getConnection();
        String query ="select from Authorities where Username=?";
        stmt = conn.prepareStatement(query);
        stmt.setString(1, username);
        rs = stmt.executeQuery();
        String authority=null;
        if(rs.next()){
            authority = rs.getString("authority");
        }
        user = new User(username, authority);
        }catch(Exception e){
            e.printStackTrace();
        }finally{
                conn.close();
                stmt.close();

        }
        return user;
    }

    public boolean update(User user, DataSource dataSource) throws SQLException {
        Connection conn = null;
        PreparedStatement stmt = null;

        try{
            conn = dataSource.getConnection();
            String Query = "update Authorities set Authority=? where Username=?";
            stmt = conn.prepareStatement(Query);
            stmt.setString(1, user.getUsername());
            stmt.setString(2, user.getAuthority());


            return stmt.execute();

        }finally{
                conn.close();
                stmt.close();
        }

    }
}

和更新jsp ..

<form action="${pageContext.request.contextPath}/Controller" >

<table>
<tbody>
<tr>
        <td><label>User name</label></td>  
        <td><input type="text" name="username" value="${user.Username }"></td>
</tr>
<tr>
        <td><label>Authority</label></td> 
        <td><input type="text" name="authority" value="${user.Authority }"><td>
</tr>

<tr>
<td><input type="submit" value="Update"></tr>
<tr>
<input type="hidden" name="page" value="update">
<input type="hidden" name="action" value="submit">
<input type="hidden" name="username" value="${user.Username }">
</tbody>
</table>

</form>

会出现什么问题......