java - 按下按钮时无法保存到数据库

Question

我有这样一个面板中的按钮代码:

    try{
        Koneksi objKoneksi = new Koneksi();
        Connection kon = objKoneksi.bukaKoneksi();
        Statement stat = kon.createStatement();
        String query = "insert into transaksi(invoiceno,kode,nama,jumlah,harga,total) values('"
                +Invoice.getText()+"','"
                +Kode.getText()+"','"
                +Nama.getText()+"','"
                +Jumlah.getText()+"','"
                +Harga.getText()+"','"
                +Total.getText()+"','";
        int rows = stat.executeUpdate(query);

        if(rows==1){
            JOptionPane.showMessageDialog(this,"Data sudah tersimpan");
            kon.close();
        }
    }
    catch(SQLException e){}
}

还有一个连接类:

http://pastebin.com/8vZpw9Ek

和语句类:

http://pastebin.com/VK358WJZ

(很抱歉没有在这里发布代码。我在预格式化文本 block 上遇到了一些问题)

当我按下按钮将数据保存到数据库时，出现了错误:

Connection success:
You are not connected to database
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javafinalproject.Aplikasi.SaveActionPerformed(Aplikasi.java:184)
at javafinalproject.Aplikasi.access$200(Aplikasi.java:15)
at javafinalproject.Aplikasi$3.actionPerformed(Aplikasi.java:83)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$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:6516)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6281)
at java.awt.Container.processEvent(Container.java:2229)dd

还有很多

有人可以帮我吗？先谢谢

Answer 1

这里发生异常:

catch (Exception ex) {
    System.out.println("You are not connected to database");
    return null;
}

你正在抑制它，你应该通过 ex.printStackTrace() 显示它。无论如何，该方法随后返回 null，这会在此处导致 NullPointerException:

Statement stat = kon.createStatement();
// --------------^^^

更新:

放在这里:

catch (Exception ex) {
    System.out.println("You are not connected to database");
    ex.printStackTrace();
    return null;
}

_{PS:你最好的办法是去和你的老师/教授谈谈，看来你缺乏解决这个问题所需的基本知识。}