Question

我正在尝试在学生信息系统中运行一个项目。我实际上已经将数据库从ms访问（accdb）转换为mysql并与我在wampserver中的java应用程序连接。我有两个用户角色，即管理员和学生。但奇怪的是，在将netbeans连接到wampserver之后，我只能通过学生用户详细信息登录，但不能使用管理员详细信息。尝试使用管理员详细信息登录时，会抛出无效的用户名或密码异常。主类登录代码如下所示：

import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPasswordField;
import javax.swing.JTextField;

public class Login extends JFrame implements ActionListener {

Container c = getContentPane();
private JButton btnLogin,  btnCancel;
private JLabel lblUName,  lblPasswd;
private JTextField txtUName;
private JPasswordField txtPasswd;

public Login() {
    super("Login ...");
    this.setSize(350, 200);
    this.setLayout(null);
    this.setResizable(false);
    this.setLocation((Settings.getScreenSize().width / 2) - 175, (Settings.getScreenSize().height / 2) - 150);
    this.setDefaultCloseOperation(EXIT_ON_CLOSE);

    lblUName = new JLabel("Username");
    lblPasswd = new JLabel("Password");
    txtUName = new JTextField();
    txtPasswd = new JPasswordField();
    btnLogin = new JButton("Login");
    btnCancel = new JButton("Cancel");
    lblUName.setBounds(50, 40, 140, 25);
    txtUName.setBounds(150, 40, 130, 25);
    lblPasswd.setBounds(50, 80, 140, 25);
    txtPasswd.setBounds(150, 80, 130, 25);
    btnLogin.setBounds(50, 120, 100, 25);
    btnCancel.setBounds(180, 120, 100, 25);
    btnLogin.addActionListener(this);
    btnCancel.addActionListener(this);
    this.add(lblUName);
    this.add(lblPasswd);
    this.add(txtUName);
    this.add(txtPasswd);
    this.add(btnLogin);
    this.add(btnCancel);
}//constructor closed
public void actionPerformed(ActionEvent e) {
    if (e.getSource() == btnLogin) {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/anu?zeroDateTimeBehavior=convertToNull","root","root");
            try {
                Statement st = con.createStatement();
                ResultSet rs = st.executeQuery("SELECT * FROM UAD WHERE Username='" + txtUName.getText() +
                        "' and Password='" + txtPasswd.getText() + "'");
                if (rs.next()) {
                    if (rs.getString(3).equals("Student")) {
                        userMDI frm = new userMDI();
                        frm.setVisible(true);
                    } else {                            
                        new frmAdminMDI().setVisible(true);
                    }
                    this.dispose();
                }else{
                    JOptionPane.showMessageDialog(null,"Invalid username or password","Invalid",JOptionPane.ERROR_MESSAGE);
                }
                con.close();

            } catch (Exception ex) {
                JOptionPane.showMessageDialog(null, "Invalid username or password", "Invalid", JOptionPane.ERROR_MESSAGE);
                txtUName.setText("");
                txtPasswd.setText("");
            }//inner try catch closed
        } catch (Exception x) {
            JOptionPane.showMessageDialog(null, "Unable to connect to the database", "Connection error", JOptionPane.ERROR_MESSAGE);
        }//outer try catch closed
    }//if closed

    if (e.getSource() == btnCancel) {
        System.exit(0);
    }//if closed
}//actionPerformed() closed
public static void main(String args[])    {
    new Login().setVisible(true);
}
}//class closed

用户表是：

使用printStackTrace（）;

后抛出的异常

java.lang.NullPointerException
at javax.swing.ImageIcon.<init>(ImageIcon.java:217)
at frmAdminMDI.<init>(frmAdminMDI.java:40)
at Login.actionPerformed(Login.java:67)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
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:6535)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6300)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4891)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
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)

这里是＆＃34; frmAdminMDI.java＆＃34;的代码：

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.ImageIcon;
import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;
import javax.swing.KeyStroke;

public class frmAdminMDI extends JFrame implements ActionListener {

private JMenuBar menubar;
private JMenu mnuAccounts;
private JMenu mnuStdDetails;
private JMenu mnuView;
private JMenu mnuOptions;
private JMenu mnuTools;
private JMenuItem mnuNewUser;
private JMenuItem mnuEditUser;
private JMenuItem mnuDeleteUser;
private JMenuItem mnuNewReg;
private JMenuItem mnuEditReg;
private JMenuItem mnuDelDetails;
private JMenuItem mnuEditMark;
private JMenuItem mnuViewStdDetails;
private JMenuItem mnuMemList;
private JMenuItem mnuMarkList;
private JMenuItem mnuAddSubs,mnuEditSubs,mnuDelSubs;
private JMenuItem mnuSubAlloc;
private JMenuItem mnuCalc,  mnuNotepad;
public static JDesktopPane desktop;

public frmAdminMDI() {
    super("Student management System");
    this.setSize(Settings.getScreenSize().width, Settings.getScreenSize().height - 30);
    this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    setIconImage(new ImageIcon(ClassLoader.getSystemResource("images/appicon.png")).getImage());
    setExtendedState(MAXIMIZED_BOTH);
    desktop = new JDesktopPane();
    menubar = new JMenuBar();
    mnuAccounts = new JMenu("Accounts");
    mnuStdDetails = new JMenu("Student details");
    mnuView = new JMenu("View");
    mnuOptions=new JMenu("Options");
    mnuTools = new JMenu("Tools");

    mnuNewUser = new JMenuItem("New User");
    mnuEditUser = new JMenuItem("Edit User");
    mnuDeleteUser = new JMenuItem("Delete User");
    mnuNewReg = new JMenuItem("New Registration");
    mnuEditReg = new JMenuItem("Edit Registration");
    mnuDelDetails = new JMenuItem("Delete Details");
    mnuEditMark = new JMenuItem("Edit Mark");
    mnuViewStdDetails = new JMenuItem("Student Details");
    mnuMemList = new JMenuItem("Member List");
    mnuMarkList = new JMenuItem("Mark List");
    mnuAddSubs=new JMenuItem("Add Subjects");
    mnuEditSubs=new JMenuItem("Edit Subjects");
    mnuDelSubs=new JMenuItem("Delete Subjects");
    mnuSubAlloc=new JMenuItem("Subject Allocation");
    mnuNotepad = new JMenuItem("Calculator");
    mnuCalc = new JMenuItem("Calculator");

    mnuAccounts.add(mnuNewUser);
    mnuNewUser.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_F2, KeyEvent.ALT_MASK));
    mnuNewUser.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/user.png")));
    mnuAccounts.add(mnuEditUser);
    mnuEditUser.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_F3, KeyEvent.ALT_MASK));
    mnuEditUser.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/editusr.png")));
    mnuAccounts.addSeparator();
    mnuAccounts.add(mnuDeleteUser);
    mnuDeleteUser.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_F4, KeyEvent.ALT_MASK));
    mnuDeleteUser.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/delusr.png")));
    mnuStdDetails.add(mnuNewReg);
    mnuNewReg.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_N, KeyEvent.CTRL_MASK));
    mnuNewReg.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/newreg.png")));
    mnuStdDetails.add(mnuEditReg);
    mnuEditReg.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_E, KeyEvent.CTRL_MASK));
    mnuEditReg.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/editreg.png")));
    mnuStdDetails.add(mnuDelDetails);
    mnuDelDetails.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_D, KeyEvent.CTRL_MASK));
    mnuDelDetails.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/delreg.png")));
    mnuStdDetails.addSeparator();
    mnuStdDetails.add(mnuEditMark);
    mnuEditMark.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_M, KeyEvent.CTRL_MASK));
    mnuEditMark.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/editmark.png")));
    mnuView.add(mnuMarkList);
    mnuMarkList.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_L, KeyEvent.CTRL_MASK));
    mnuMarkList.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/marklist.png")));
    mnuView.add(mnuMemList);
    mnuMemList.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_S, KeyEvent.CTRL_MASK));
    mnuMemList.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/memlist.png")));
    mnuView.add(mnuViewStdDetails);
    mnuViewStdDetails.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_T, KeyEvent.CTRL_MASK));
    mnuViewStdDetails.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/stddet.png")));
    mnuOptions.add(mnuAddSubs);
    mnuOptions.add(mnuEditSubs);
    mnuOptions.add(mnuDelSubs);
    mnuOptions.addSeparator();
    mnuOptions.add(mnuSubAlloc);        
    mnuTools.add(mnuCalc);
    mnuCalc.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_C, KeyEvent.CTRL_MASK));
    mnuCalc.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/calc.png")));
    mnuTools.add(mnuNotepad);
    mnuNotepad.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_U, KeyEvent.CTRL_MASK));
    mnuNotepad.setIcon(new ImageIcon(ClassLoader.getSystemResource("images/notepad.png")));


    menubar.add(mnuAccounts);
    menubar.add(mnuStdDetails);
    menubar.add(mnuView);
    menubar.add(mnuOptions);
    menubar.add(mnuTools);
    mnuNewUser.addActionListener(this);
    mnuEditUser.addActionListener(this);
    mnuDeleteUser.addActionListener(this);
    mnuNewReg.addActionListener(this);
    mnuEditReg.addActionListener(this);
    mnuDelDetails.addActionListener(this);
    mnuEditMark.addActionListener(this);
    mnuMarkList.addActionListener(this);
    mnuMemList.addActionListener(this);
    mnuViewStdDetails.addActionListener(this);
    mnuAddSubs.addActionListener(this);
    mnuEditSubs.addActionListener(this);
    mnuDelSubs.addActionListener(this);
    mnuSubAlloc.addActionListener(this);
    mnuCalc.addActionListener(this);        
    mnuNotepad.addActionListener(this);
    this.setJMenuBar(menubar);
    this.add(desktop);
}//constructor closed
public void actionPerformed(ActionEvent e) {
    try {
        if (e.getSource() == mnuNewUser) {
            NewUserReg frm = new NewUserReg();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if (e.getSource() == mnuEditUser) {
            Edituser frm = new Edituser();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if (e.getSource() == mnuDeleteUser) {
            Deleteuser frm = new Deleteuser();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if (e.getSource() == mnuNewReg) {
            NewStdReg frm = new NewStdReg();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if (e.getSource() == mnuEditReg) {
            EditStdReg frm = new EditStdReg();
            desktop.add(frm);
            frm.setVisible(true);

        }
        if (e.getSource() == mnuDelDetails) {
            Deletedetails frm = new Deletedetails();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if (e.getSource() == mnuMarkList) {
            viewMark frm = new viewMark();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if (e.getSource() == mnuEditMark) {
            EditMark frm = new EditMark();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if (e.getSource() == mnuCalc) {
            Runtime.getRuntime().exec("calc.exe");
        }
        if (e.getSource() == mnuNotepad) {
            Runtime.getRuntime().exec("notepad.exe");
        }
        if (e.getSource() == mnuMemList) {
            MembersList frm = new MembersList();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if (e.getSource() == mnuViewStdDetails) {
            User frm = new User();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if(e.getSource()==mnuAddSubs){
            AddSubjects frm=new AddSubjects();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if(e.getSource()==mnuEditSubs){
            EditSubjects frm=new EditSubjects();
            desktop.add(frm);
            frm.setVisible(true);
        }
         if(e.getSource()==mnuDelSubs){
            DelSubjects frm=new DelSubjects();
            desktop.add(frm);
            frm.setVisible(true);
        }
        if(e.getSource()==mnuSubAlloc){
            SubjectAllocation frm=new SubjectAllocation();
            desktop.add(frm);
            frm.setVisible(true);
        }
    } catch (Exception ex) {
        JOptionPane.showMessageDialog(new JFrame(), "Error, Cannot load window" + ex.toString(), "Error", JOptionPane.ERROR_MESSAGE);
    }//try catch closed
}//actionPerformed() closed
} //class closed

将java连接到mysql数据库后，无法通过管理员详细信息登录

0 个答案: