java - JDBC 空指针异常

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 9 年前。

我在 swing 中编写了一段代码，其中在 jTextFields 中插入了文本。但是当我尝试将它们插入数据库时​​，它在“Driver Connected”之后给出 NullPointerException。以下是我的 JDBC 代码:

    Connection conn = null;
    PreparedStatement pst = null;
    ResultSet rs = null;
    try{

        Class.forName("oracle.jdbc.OracleDriver");
        System.out.println("Driver Loaded.");
        conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl",                           "usname", "pass");
        System.out.println("Driver Connected.");

        String insert = "INSERT INTO directorsdb values (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)";
        pst=conn.prepareStatement(insert);

        pst.setString(1, dirname.getText());
        pst.setString(2, jDateChooser1.getDate().toString());
        pst.setString(3, DIN.getText());
        pst.setString(4, PAN.getText());
        pst.setString(5, UIN.getText());
        pst.setString(6, birthplace.getText());
        pst.setString(7, passportno.getText());
        pst.setString(8, dlicense.getText());
        pst.setString(9, nationality.getText());
        pst.setString(10, occupation.getText());
        pst.setString(11, occupationcompany.getText());
        pst.setString(12, designation.getText());
        pst.setString(13, qualification.getText());
        pst.setString(14, officeadd.getText());
        pst.setString(15, residentialadd.getText());
        pst.setString(16, contacthome.getText());
        pst.setString(17, contactwork.getText());
        pst.setString(18, contactmobile.getText());
        pst.setString(19, emailper.getText());
        pst.setString(20, emailwork.getText());
        pst.setString(21, emailother.getText());
        pst.setString(22, secretaryname.getText());
        pst.setString(23, secretarycontact.getText());
        pst.setString(24, secretaryemail.getText());
        pst.setString(25, buttonGroup1.getSelection().getActionCommand());
        pst.setString(26, jDateChooser2.getDate().toString());
        pst.setString(27, fathername.getText());
        pst.setString(28, mothername.getText());
        pst.setString(29, jDateChooser3.getDate().toString());
        pst.setString(30, posiionboard.getText());
        pst.setString(31, jDateChooser4.getDate().toString());
        pst.setString(32, cessationreason.getText());
        pst.setString(33, buttonGroup2.getSelection().getActionCommand());
        pst.setString(34, buttonGroup3.getSelection().getActionCommand());
        pst.setString(35, aboutd.getText());

        pst.execute();


    }catch(SQLException e){
        System.err.println(e.fillInStackTrace());
    }
     catch(ClassNotFoundException ex){
         System.err.println(ex);
     } finally{                                 // != means NOT EQUAL TO
        if (rs != null){
            try {
                rs.close();
            } catch (SQLException ex) {
                System.err.println(ex);
            }

            }
        if (pst != null){
            try {
                pst.close();
            } catch (SQLException ex) {
                System.err.println(ex);
            }
        }
        if (conn != null){
            try {
                conn.close();
            } catch (SQLException ex) {
                System.err.println(ex);
            }
         }
     }

以下是异常(exception)情况:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at DirectorDB.NewEntry.jButton1ActionPerformed(NewEntry.java:882)
at DirectorDB.NewEntry.access$1800(NewEntry.java:28)
at DirectorDB.NewEntry$19.actionPerformed(NewEntry.java:738)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$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:3320)
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:735)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
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:708)
at java.awt.EventQueue$4.run(EventQueue.java:706)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
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)

Answer 1

What appears at line 882 of NewEntry?

回复...

pst.setString(2, jDateChooser1.getDate().toString())

那么我建议jDateChooser1.getDate()为null。

您不应该使用String设置日期字段，数据库应该设置为使用适当的日期/时间数据类型，并且您应该尝试使用pst.setDate(.. .) 相反。

这将以易于加载的方式存储日期/时间值。您应该注意 Date#toString 将以当前本地指定的格式存储日期，这使得加载和解析变得困难

如果您无法使用数据库中的实际日期值，那么您应该使用更像...的东西

Date value = jDateChooser1.getDate();
pst.setString(2, value == null ? null : value.toString());

更好的是，使用 SimpleDateFormat 将 String 值格式化为商定的格式