idea web工程登录出现问题

Question

读取mysql 判断对象是否存在
用户名不存在返回-1
密码错误返回-2
登录成功返回0

部分代码如下:
AccountSverlet

@WebServlet("/account")
public class AccountServlet extends HttpServlet {

    private SystemAdminService systemAdminService = new SystemAdminServiceImpl();


    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        SystemAdminDto systemAdminDto = this.systemAdminService.login(username,password);
        switch (systemAdminDto.getCode()){
            case -1:
                req.setAttribute("usernameError","用户名不存在");
                req.getRequestDispatcher("login.jsp").forward(req,resp);
                break;
            case -2:
                req.setAttribute("passwordError","密码错误");
                req.getRequestDispatcher("login.jsp").forward(req,resp);
                break;
            case 0:
                System.out.println("登录成功!");
                break;

        }
    }
}

public class SystemAdminDaoImpl implements SystemAdminDao {

    @Override
    public SystemAdmin findBYUsername(String username) {
        Connection connection = JDBCUtil.getConnection();
        String sql = "select * from system_admin where username = '"+username+"'";
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        try {
            statement = connection.prepareStatement(sql);
            resultSet = statement.executeQuery();
            if (resultSet.next()) {
                int id = resultSet.getInt(1);
                username = resultSet.getString(2);
                String password = resultSet.getString(3);
                String gender = resultSet.getString(4);
                String Purview = resultSet.getString(5);
                String Telephone = resultSet.getString(6);
                return new SystemAdmin(id,username,password,gender,Purview,Telephone);

            }
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }finally {
            JDBCUtil.release(connection,statement,resultSet);
        }
        return null;
    }
}

运行的时候不论是输入正确的用户名或者是错误密码 返回的都是用户名不存在

这种情况是问题出在哪里哇？是数据库没读取到的与原因吗？

Answer 1

页面的代码贴一下，你把这个打印出来。而且你service里干啥了

String username = req.getParameter("username");