Question

我想从MySQL数据库中打印出一列。我有一个日历系统，您可以在其中选择“从”日期“到”日期。当您选择时间段时，它应该从MySQL数据库打印出COLUMN“Allday_hours”。我正在使用javascript，AJAX和JSON。这是在调用我的servlet。我制作的第一个servlet没有打印任何东西，但它给了我一个成功。因此，在堆栈溢出的人的帮助下，代码发生了变化，看起来更正确，但现在它给了我一个失败。我制作了2个视频。有谁能看到这里有什么问题？我用于两个servlet的javascript代码

最诚挚的问候 MADS

第一个成功的servlet：视频： https://www.youtube.com/watch?v=UzdvQ4B9clw&feature=youtu.be

Servlet代码：

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;
        res.setContentType("text/html");
        PrintWriter out = res.getWriter();

        try {

            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(connectionURL, "root", ""); 
            String sql = "SELECT *, (Day_hours + (Day_minutes / 100)) AS Allday_hours FROM Workdata";
            PreparedStatement pst = connection.prepareStatement(sql);
            pst.execute(sql);
            pst.close();
        }
        catch(ClassNotFoundException e){

            out.println("Couldn't load database driver: " + e.getMessage());
        }
        catch(SQLException e){
            out.println("SQLException caught: " + e.getMessage());
        }
        catch (Exception e){
            out.println(e);
        }
        finally {

            try {
                if (connection != null) connection.close();
            }
            catch (SQLException ignored){
                out.println(ignored);
            }
        }
    }
}

此视频和代码是最新版本，它会给我一个错误。我已经//添加了新代码：视频： https://www.youtube.com/watch?v=6DO1GnjDRWk

Servlet代码：

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;
        String all_day_hours = null;                            // new code
        res.setContentType("text/html;charset=UTF-8");          // new code
        res.getWriter().write(all_day_hours);                   // new code

        try {

            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(connectionURL, "root", ""); 
            String sql = "SELECT *, (Day_hours + (Day_minutes / 100)) AS Allday_hours FROM Workdata";
            PreparedStatement pst = connection.prepareStatement(sql);
            ResultSet rs = pst.executeQuery(sql);

            if(rs.next()){                                      // new code
                 all_day_hours = rs.getString("Allday_hours");  // new code
            }                                                   // new code
            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);
            }
        }
    }
}

Javascript代码：

<form>
          <input id="startDate" />

          <input id="endDate" />
    </form>
    <div id="result"></div>
    <script>

    $(function(){
        $("#startDate").datepicker({
            dateFormat: 'yy-mm-dd',
            onSelect: function(dateText,inst){
                alert(dateText);

                $.ajax({
                      url: "../getHoursSQL",
                      type: "post",
                      data: JSON,
                      success: function(data){
                          alert("success");
                          $("#result").html(data);

                      },
                      error:function(){
                          alert("failure");
                          $("#result").html('there is error while submit');
                      }  
                    });
            }
        });
    });

    $(function(){
            $("#endDate").datepicker({
                dateFormat: 'yy-mm-dd',
                onSelect: function(dateText,inst){
                    alert(dateText);

                    $.ajax({
                          url: "../getHoursSQL",
                          type: "post",
                          data: JSON,
                          success: function(data){
                              alert("success");
                              $("#result").html(data);
                          },
                          error:function(){
                              alert("failure");
                              $("#result").html('there is error while submit');
                          }  
                        });
                }
            });
        });

</script>

Answer 1

正确答案：

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;
                                // new code
                    // new code

        try {

            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(connectionURL, "root", ""); 
            String sql = "SELECT *, (Day_hours + (Day_minutes / 100)) AS Allday_hours FROM Workdata";
            PreparedStatement pst = connection.prepareStatement(sql);

            ResultSet rs = pst.executeQuery(sql);
            String all_day_hours = null;    
            if(rs.next()){                                      // new code
                 all_day_hours = rs.getString("Allday_hours");  // new code
            }                                                   // new code
            pst.close();
            res.setContentType("text/html;charset=UTF-8");          // new code
            res.getWriter().write(all_day_hours);   
        }
        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);
            }
        }
    }
}

Servlet打印输出错误

1 个答案: