JTable+mysql数据库

Question

我想将在 jtable 上输入的信息保存到 mysql 数据库。我专门将学生的分数从 jtable 保存到数据库中。这是我的代码的 sn-p，它应该通过单击 gui 上的“保存”按钮来保存项目。

private void btnSaveActionPerformed(java.awt.event.ActionEvent evt)
{                                                                                               
  tblMarkSheet.getRowCount();
      try 
      { 

        String sql = "INSERT INTO marksheet(examName,streamName,className,termName,academicYear,pupilID,mathematics,english,kiswahili,science,SS_CRE,total) VALUES('" + cboExamName.getSelectedItem() + "','" + cboStream.getSelectedItem() + "','" + cboClass.getSelectedItem() + "','" + cboTerm.getSelectedItem() + "','" + cboAcademicYear.getSelectedItem() + "','" + Integer.parseInt(tblMarkSheet.getValueAt(row, 0).toString()) + "','" + Integer.parseInt(tblMarkSheet.getValueAt(row, 1).toString()) + "','" + Integer.parseInt(tblMarkSheet.getValueAt(row, 2).toString()) + "','" + Integer.parseInt(tblMarkSheet.getValueAt(row, 3).toString()) + "','" + Integer.parseInt(tblMarkSheet.getValueAt(row, 4).toString()) + "','" + Integer.parseInt(tblMarkSheet.getValueAt(row, 5).toString()) + "','" + Integer.parseInt(tblMarkSheet.getValueAt(row, 6).toString()) + "') ";
        stmt.execute(sql);
        JOptionPane.showMessageDialog(null, "Marks Saved successfully!");

      }
      catch (Exception e) 
      {
       JOptionPane.showMessageDialog(this, e.getMessage());
       e.printStackTrace();
      }
}  

我收到以下错误：

java.lang.NullPointerException
    at AmsProject.MarkSheet.btnSaveActionPerformed(MarkSheet.java:445)
    at AmsProject.MarkSheet.access$100(MarkSheet.java:18)
    at AmsProject.MarkSheet$3.actionPerformed(MarkSheet.java:185)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6505)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
    at java.awt.Component.processEvent(Component.java:6270)
    at java.awt.Container.processEvent(Container.java:2229)
    at java.awt.Component.dispatchEventImpl(Component.java:4861)
    at java.awt.Container.dispatchEventImpl(Container.java:2287)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
    at java.awt.Container.dispatchEventImpl(Container.java:2273)
    at java.awt.Window.dispatchEventImpl(Window.java:2719)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:682)
    at java.awt.EventQueue$3.run(EventQueue.java:680)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:696)
    at java.awt.EventQueue$4.run(EventQueue.java:694)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

我希望我可以在此处粘贴带有行号的代码，但我的 IDE 在显示数字时出现问题。第 445 行是这样的

System.out.println(Integer.parseInt(tblMarkSheet.getValueAt(row, 6).toString()));

第 18 行：

public class MarkSheet extends javax.swing.JFrame {

和第 185 行：

btnSaveActionPerformed(evt);

请帮帮我。我将不胜感激！

Answer 1

使用Statement#executeUpdate 进行数据库写入操作。同时使用PreparedStatement 而不是Statement 来防止SQL Injection 攻击。

根据您的更新，变量 tblMarkSheet 似乎是 null：

System.out.println(Integer.parseInt(tblMarkSheet.getValueAt(row, 6).toString()))

检查它是否已正确分配并且在actionPerformed 方法的范围内可用。例如，确保您没有在实例化它的地方创建此变量的本地实例。