Debugging JavaScript and a servlet

我是一个编程新手。这道题是为考试做准备的。我有一个servlet连接到我的MySQL数据库。此外，我有一个JavaScript。

我有两个日历，你可以选择"从"日期-"到"日期。如果我选择从2014-03-06到2014-03-10，我想打印出我在这段时间内工作了多少小时。这意味着我的servlet正在从MySQL数据库获取列"Allday_hours"。问题是，每次我选择一个日期从javascript，它只是返回所有的小时从Allday_hours。这意味着它将遍历所有列，而不是我选择的日期。

  <form>
        <input id="startDate"/>                     
        <input id="endDate"/>
    </form>
    <div id="startresult"></div>
    <div id="endresult"></div>
    <script>
    $(function(){
        $("#startDate").datepicker({
            dateFormat: 'yy-mm-dd',
            onSelect: function(dateText,inst){
                $('.selected-date').html(dateText);
                $.ajax({
                      url: "../getHoursSQL",
                      type: "post",
                      data: JSON,
                      success: function(data){
                           start: $("#startDate").val();
                          alert("success");
                          $("#startresult").html(data);
                      },
                      error:function(){
                          alert("failure");
                          $("#startresult").html('there is error while submit');
                      }  
                    });
            }
        });
    });
    $(function(){
            $("#endDate").datepicker({
                dateFormat: 'yy-mm-dd',
                onSelect: function(dateText,inst){
                    $('.selected-date').html(dateText);
                    $.ajax({
                          url: "../getHoursSQL",
                          type: "post",
                          data: JSON,
                          success: function(data){
                              end: $("#endDate").val();
                              alert("success");
                              $("#endresult").html(data);
                          },
                          error:function(){
                              alert("failure");
                              $("#result").html('there is error while submit');
                          }  
                        });
                }
            });
        });
</script>

        package WorkPackage;
import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
@WebServlet("/getHoursSQL")
public class getHoursSQL extends HttpServlet{
    private static final long serialVersionUID = 1L;
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }
    public void doPost(HttpServletRequest req, HttpServletResponse res) 
        throws ServletException, IOException{
        String connectionURL = "jdbc:mysql://localhost/NekiWork";
        Connection connection=null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(connectionURL, "root", ""); 
            String sql = "SELECT *, (Day_hours + (Day_minutes / 60)) AS Allday_hours FROM Workdata WHERE startDate='?' AND endDate='?'"; 
            PreparedStatement pst = connection.prepareStatement(sql);
                pst.setXXX(1,startDate);
                pst.setXXX(2,endDate);
                ResultSet rs = pst.executeQuery(sql);
            float Allday_hours_sum = 0;
                while (rs.next()){                                      
                    Allday_hours_sum += rs.getFloat("Allday_hours"); 

            }   
                res.setContentType("text/html;charset=UTF-8");          
                res.getWriter().print(Allday_hours_sum); 
                String startDate = req.getParameter("startDate");
                String endDate= req.getParameter("endDate");
            pst.close();

        }
        catch(ClassNotFoundException e){
            System.out.println("Couldn't load database driver: " + e.getMessage());
        }
        catch(SQLException e){
            System.out.println("SQLException caught: " + e.getMessage());
        }
        catch (Exception e){
            System.out.println(e);
        }
        finally {
            try {
                if (connection != null) connection.close();
            }
            catch (SQLException ignored){
                System.out.println(ignored);
            }
        }
    }
}