Question

我有一个名为LoginScreen的jframe用于连接到DB。一个文本字段用于uname输入，一个密码字段用于密码输入，一个登录按钮和一个用于记住用户名值的复选框。我希望当用户单击Uname Remember复选框并尝试登录时，如果从DB值接受uname和密码，则必须将其存储在pref键中。让我分享代码;

public class LoginScreen extends javax.swing.JFrame {

    /**
     * Creates new form LoginScreen 
     */
    public LoginScreen() {
        initComponents(); //initialize components
        if ( "null" == PREF_NAME){
        rememberCheckBox.setSelected(false);
        }
        else if ("null" != PREF_NAME){
        rememberCheckBox.setSelected(true);    
        }

        if (true == rememberCheckBox.isSelected()){
        unameTextField.setText(PREF_NAME);
        }
        else if(false == rememberCheckBox.isSelected()){
        unameTextField.setText("your user name");
        }
    }

Preferences prefs = Preferences.userNodeForPackage(rememberexample.LoginScreen.class);
String PREF_NAME = "null";

private void loginButtonActionPerformed(java.awt.event.ActionEvent evt) {                                            
        // TODO add your handling code here:

        try {  
        Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
        String connectionUrl = "jdbc:sqlserver://192.168.100.100;" + "databaseName=ExampleDB;" + "user=" + unameTextField.getText() + ";" + "password=" + new String (jPasswordField1.getPassword()) + ";"; 
        Connection con = DriverManager.getConnection(connectionUrl);
            if (true == rememberCheckBox.isSelected()){
            prefs.put(PREF_NAME, unameTextField.getText());
            System.out.println(PREF_NAME);
            }
            else if (false == rememberCheckBox.isSelected()){
            prefs.remove(PREF_NAME);
            System.out.println(PREF_NAME);
            }
        con.close();
        }
        catch (SQLException e) {
            JOptionPane.showMessageDialog(this, "Wrong id or password!!");
        }
        catch (ClassNotFoundException cE) {
            System.out.println("Class Not Found Exception: "+ cE.toString());
        }
    }   

public static void main(String args[]) {

java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new LoginScreen().setVisible(true);
            }
        });
    }

private javax.swing.JPasswordField jPasswordField1;
private javax.swing.JButton loginButton;
private javax.swing.JCheckBox rememberCheckBox;
private javax.swing.JTextField unameTextField;

但PREF_NAME始终返回null。我已经添加了一个控件来执行按钮操作，如您所见。的System.out.println（PREF_NAME）;单击按钮时返回null。有什么想法吗？

Answer 1

你放了：

 String PREF_NAME = "null";

然后你永远不会改变它的价值（你不应该，稍后再看..）并且你正在打印出来：

 System.out.println(PREF_NAME);

==＆GT;显然你得到“null”作为输出

你应该做什么：

 final String PREF_NAME = "pref_name"; //define the name for your key

然后：

 prefs.put(PREF_NAME, unameTextField.getText()); //put something in your preference using your key
 System.out.println(prefs.get(PREF_NAME, "no value")); //output the preference *value* not the key

请参阅documentation

用于记住用户信息的Java首选项

1 个答案: