Throwing Exceptions method from method

Question

I have a Login Method that is triggered by JButton Actionperformed.

private void loginButtonActionPerformed(java.awt.event.ActionEvent evt) {

    try {

        Users userData = userDAO.login(Integer.parseInt(loginUserId.getText()), String.valueOf(loginUserPassword.getPassword()));            

    } catch (SQLException ex) {
        LOGGER.log(Level.SEVERE, ex.toString(), ex);
        JOptionPane.showMessageDialog(null, "Error SQL: Please Contact your System Administrator", cf.WINDOW_TITLE, JOptionPane.ERROR_MESSAGE);  
    } catch (NullPointerException e) {
        JOptionPane.showMessageDialog(null, e.getMessage(), cf.WINDOW_TITLE, JOptionPane.ERROR_MESSAGE);  
    } catch (NumberFormatException e) {            
        JOptionPane.showMessageDialog(null, "Pls write a number", cf.WINDOW_TITLE, JOptionPane.ERROR_MESSAGE);  
    }
}

Here is my Method that returns an Object from the database.

public Users login(int userId, String password) throws NumberFormatException, SQLException , NullPointerException {

    SQL sql = new SQL();
    query = sql.createPStatement(cf.SELECT_USER_BY_LOGIN_DATA);        
    query.setInt(1, userId);
    query.setString(2, password);
    ResultSet resultSet = query.executeQuery();
    try {
        if (!resultSet.isBeforeFirst()) {              
            throw new NullPointerException("User Not Found");
        }
        while (resultSet.next()) {
            Users newLoggedUser = new Users();
            //Set Object Values
            return newLoggedUser;
        }
    } catch (SQLException e) {
        LOGGER.log(Level.SEVERE, e.toString(), e);
        throw e;
    }  
catch (NullPointerException e) {
        LOGGER.log(Level.SEVERE, e.toString(), e);
        throw e;
    } catch (NumberFormatException e) {
  LOGGER.log(Level.SEVERE, e.toString(), e);
        throw e;
    } finally {
        SQLUtils.closeQuietly(sql.dbConection());
        SQLUtils.closeQuietly(resultSet);
        SQLUtils.closeQuietly(query);            
    }
    return null;
}  

I have to show multiple error messages to the USER accorgding to:

• User not found (No SQL result);
• Type Letters instead of numbers
• SQL Error.

I have some questions about this:

1. Should I Stop the app to doing more actions Where my Results/Objects are NULL , using throw new NullPointerException("User Not Found");

2. Is safely to use those exceptions to send User Messages, like in the case of Object is null ("User not Found"), and throw them by the DAO Method to be catched/Displayed by the JButton ActionPerformed try/Catch?

3. Where I should log the exceptions, in the DAO Method? , or ActionPerformed try/Catch?.

4. Should I throw e; again in DAO Method to be catched by ActionPerformed try/Catch?

Like Always thank you very much for your help.

Answer 1

1. IMO the best way to handle would be to create your own custom exception (extends Exception) like

   public class LoginException extends Exception{
     public LoginException(Exception cause, String message) {
       ..
     }
   }
   

You can use the message parameter to specify what to display to the client.

Wrap all of your possible login exceptions thru this, and declare it as thrown by your DB method

2. Sure, It's safe. And many programs do this. But it's better to try to clarify the problem to the user.

3. This requires us to state an opinion, which is off-topic. You could do it either way. But me, I'd do it in the actionPerformed, as the button click starts the "transaction".

4. Same answer as 3