login problem

[nasha shaharan]

Hi all!
i have a question.
i have a standalone java swing program that i use with postgreSQL jdbc. it has a login page which can compare the textfield with the value in database.

this is part of my code:

private void login(ActionEvent e) {
		try
		{
			Class.forName("org.postgresql.Driver"); 
			//gets a connection
			conn = DriverManager.getConnection("jdbc:postgresql://localhost:5432/test","postgres","870127");
			stmt = conn.createStatement();
			ResultSet results = stmt.executeQuery("select * from " + tableName);
			
			while(results.next())
			{
				String username = results.getString(2);
				String password = results.getString(3);
				String login = loginTextField.getText();
				String pass = new String(passwordTextField.getPassword());
				
				//validate login and password here. validity will be done by sending login/password to the server
				if (login.equals(username) && pass.equals(password)) {
					System.out.println("login successful");
					showButtonsView();
				} 	
				else {
					JOptionPane.showMessageDialog(this,"Incorrect login or password","Error",JOptionPane.ERROR_MESSAGE);
					loginTextField.setText("");
					passwordTextField.setText("");
					loginTextField.requestFocusInWindow();
				}
				
			}
			results.close();
			stmt.close();
		}
		catch (Exception ex)
		{
			ex.printStackTrace();
		}
	}
		

problem is, when i entered the correct username and password, the "incorrect login and password" warning JOption still pops out!
can you tell me how to fix this? thank you in advance!

[Andrew Monkhouse]

Are you storing the password unencrypted in the database?

Generally speaking, selecting * from a table is a bad idea. Similarly getting a value from the resultset based on the index is a bad idea. There is the potential here that you are getting the wrong values. I strongly recommend you change that to (changing field names as appropriate):

			ResultSet results = stmt.executeQuery("select username, password from " + tableName);

			// ...

				String username = results.getString("username");
				String password = results.getString("password");

[nasha shaharan]

yes, it's unencrypted..
ok i will try what you suggested..thanks

edit: i tried that but it didn't solve the problem..can you please tell me whats wrong?

[Andrew Monkhouse]

Is it possible that you have more than one row in your table? If so, is the display of the dialog in the correct place in your code?

[nasha shaharan]

um, yeah i have 3 rows of data in db..

[Andrew Monkhouse]

OK, let's assume the 3 records are:

user-a/password-a

user-b/password-b

user-c/password-c

Now if you were to enter "user-b/password-b" - what would happen on the very first loop through your code?

Alternatively, if you had entered "user-a/password-a", what would have happened on the second loop through your code? (Why do you allow a second loop through your code?)

Which goes back to what I was saying earlier - is your code that displays the "Incorrect login or password" in the right place? Is there a better way of determining whether any of the usernames/passwords matched before showing that?

[nasha shaharan]

i think i put the if else code in the wrong place..because it iterates my record (i think)..
this is because when i log in..the incorrect password warning flashes 2 times when i entered user-a/password-a

can you suggest where i was to put the if else code?

[venkat prathap]

i would suggest change the query to

ResultSet results = stmt.executeQuery("select * from " + tableName +" where username ='"+login+"'");

hope...It might help you..

[mallikarjun dontamsetti]

Try this using prepared statement
PreparedStatement pstmt;

String sql="Select * from login where username=? and password=?"
pstmt=conn.prepareStatement(sql);
pstmt.setString(1,username);
pstmt.setString(2,password);
ResultSet rs=pstmt.executeQuery();

[nasha shaharan]

oh i solved it!
thanks andrew and venkat!

anyways this is my code now:

private void login(ActionEvent e) {
		try
		{
			Class.forName("org.postgresql.Driver"); 
			//gets a connection
			conn = DriverManager.getConnection("jdbc:postgresql://localhost:5432/test","postgres","870127");
			stmt = conn.createStatement();
			String login = loginTextField.getText();
			String pass = new String(passwordTextField.getPassword());
			ResultSet results = stmt.executeQuery("select username, password from " + tableName +" where username ='"+login+"'");
			String username = "";
			String password = "";
			
			while(results.next())
			{
				username = results.getString("username");
				password = results.getString("password");
			}
				//validate login and password here. validity will be done by sending login/password to the server
				if (login.equals(username) && pass.equals(password)) {
					System.out.println("login successful");
					showButtonsView();
				} 	
				else {
					JOptionPane.showMessageDialog(this,"Incorrect login or password","Error",JOptionPane.ERROR_MESSAGE);
					loginTextField.setText("");
					passwordTextField.setText("");
					loginTextField.requestFocusInWindow();
				}
				
			
			results.close();
			stmt.close();
		}
		catch (Exception ex)
		{
			ex.printStackTrace();
		}
	}

[Swastik Dey]

ResultSet results = stmt.executeQuery("select username, password from " + tableName +" where username ='"+login+"'");

The above code it self will satisfy your purpose, then what is the below code. Why are you checking once again?

 if (login.equals(username) && pass.equals(password))

just by doing this your purpose should get solved, with an assumption that username and password forms a unique record

ResultSet results = stmt.executeQuery("select username, password from " + tableName +" where username ='"+login+"'");
if(results.next()){
  //valid login
}
else{
  //invalid login
}

[nasha shaharan]

Swastik Dey wrote:

ResultSet results = stmt.executeQuery("select username, password from " + tableName +" where username ='"+login+"'");

The above code it self will satisfy your purpose, then what is the below code. Why are you checking once again?

 if (login.equals(username) && pass.equals(password))

just by doing this your purpose should get solved, with an assumption that username and password forms a unique record

ResultSet results = stmt.executeQuery("select username, password from " + tableName +" where username ='"+login+"'");
if(results.next()){
  //valid login
}
else{
  //invalid login
}

im doing that because i wanna compare if the user inputs the right set of username and password.
if i follow your suggestion, then how to compare the password part?

[Paul Sturrock]

I think Swastik is just misreading your SQL - assumign it check by both username and password. If you have already matched your user by username and password in SQL, what extra functionality does your check in Java provide? You only check by username; if you change your SQL to check by both credentials your Java code is redundant.

[Swastik Dey]

Paul is right, I just misread it. It should be

ResultSet results = stmt.executeQuery("select username, password from " + tableName +" where username ='"+login+"' and password='"+password+"'");

However it would be better to use PreparedStatement.

[Abraham Moyo]

I must agree with Paul.

Imagine what would happen if you had 2 users (table row entries) with the same username but different passwords.....