通过Java注册到Mysql数据库失败

您好，我正在创建一个小应用程序，我想在其中注册用户到数据库。看起来不错，但是它告诉我我的驱动程序有问题，我无法发现它。

我的代码：

private void createEventListenerDBProperties() {
        dbSubmitBtn.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {

                    if (dbDriverChooser.getSelectedItem().equals("com.mysql.jdbc.Driver")) {
                        driver = (String) dbDriverChooser.getSelectedItem();
                        port = dbPortField.getText();
                        host = "jdbc:mysql://" + hostField.getText() + ":" + port + "/";
                    } else if (dbDriverChooser.getSelectedItem().equals("oracle.jdbc.driver.OracleDriver")) {
                        driver = (String) dbDriverChooser.getSelectedItem();
                        port = dbPortField.getText();
                        host = "jdbc:oracle:thin:@" + hostField.getText() + ":" + port + ":";
                    } else if (dbDriverChooser.getSelectedItem().equals("org.postgresql.Driver")) {
                        driver = (String) dbDriverChooser.getSelectedItem();
                        port = dbPortField.getText();
                        host = "jdbc:postgresql://" + hostField.getText() + ":" + port + "/";
                    } else {
                        driver = (String) dbDriverChooser.getSelectedItem();
                        host = "jdbc:sqlite:";
                    }
                    db = dbnameField.getText();
                    dbuser = dbUsernameField.getText();
                    dbpassword = new String(dbPasswordField.getPassword());
                    main.remove(dbProperties);
                    main.add(register);
                    main.revalidate();
                }
        });
    }

我的连接方法：

private Connection instanciateDB() {
        Connection con = null;
        try {
            Class.forName(driver).newInstance();
            con = DriverManager.getConnection(host + db, dbuser, dbpassword);
            System.out.println("Connection Established");
        } catch (ClassNotFoundException | SQLException | InstantiationException |IllegalAccessException e) {
            System.out.println("Connection not Established");
            JOptionPane.showMessageDialog(MainFrame.this, e.getMessage(), "Error", JOptionPane.ERROR_MESSAGE);
        }
        return con;
    }

我的注册方法：

private void setupRegisterEventListener() {
        registerBtn.addActionListener((ActionEvent e) -> {

                try {
                    conn = instanciateDB();
                    pst = conn.prepareStatement("insert into usersinfo(username, password) values(?,?)");
                    pst.setString(1, leftFirstText);
                    pst.setString(2, new String(leftSecondText));
                    int x = pst.executeUpdate();
                } catch (SQLException ex) {
                    JOptionPane.showMessageDialog(MainFrame.this, "Registration Failed");
                    System.out.println(ex.getMessage());
                }
                JOptionPane.showMessageDialog(MainFrame.this, "Registration Successful", "Success", JOptionPane.PLAIN_MESSAGE);
        });
    }

它给了我错误com.mysql.jdbc.Driver，我不知道为什么使用instanciateDB方法。

Connection not Established
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at ijae4.xdrako00.MainFrame.lambda$setupRegisterEventListener$0(MainFrame.java:126)
    at ijae4.xdrako00.MainFrame$$Lambda$13/1389133897.actionPerformed(Unknown Source)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
    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:6525)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
    at java.awt.Component.processEvent(Component.java:6290)
    at java.awt.Container.processEvent(Container.java:2234)
    at java.awt.Component.dispatchEventImpl(Component.java:4881)
    at java.awt.Container.dispatchEventImpl(Container.java:2292)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
    at java.awt.Container.dispatchEventImpl(Container.java:2278)
    at java.awt.Window.dispatchEventImpl(Window.java:2739)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746)
    at java.awt.EventQueue.access$400(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:697)
    at java.awt.EventQueue$3.run(EventQueue.java:691)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:719)
    at java.awt.EventQueue$4.run(EventQueue.java:717)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

有任何想法吗？

先感谢您！