检查用户名和密码时出错

Question

Im currently attempting to make a login system in Java and SQL and am currently getting an error.

PreparedStatement s1 = con.prepareStatement("SELECT * FROM dbo.Logins WHERE Username=? AND Password=?");
s1.setString(1,loginUsername);
s1.setString(2, loginPassword.toString());
ResultSet rs = s1.executeQuery();

if(rs.next()){
    JOptionPane.showMessageDialog(null, "User Found");
}
else{
    JOptionPane.showMessageDialog(null, "Error");
}

When I run that snippet of code it always displays the else part of the if/else and im not sure why. Thank in advance.

Edit: Yes the DB is populated with users. Edit2: I changed the function to require two string args.

Answer 1

You must try to use while(rs.next()) instead of if(rs.next()) .

If that does not work, does your DB (which you have mentioned is populated), contain those particular values of username and password that you are searching for ? If not, that may be the problem.

If that too does not work, you may have closed some objects (eg. s1.close() or con.close() ) where you shouldn't. For further help on that you will need to provide a more detailed flow of what you have done in the whole code.

Answer 2

You can fetch number of rows available in your table for given query and if it is great than 0 it will execute User Found statement.

PreparedStatement s1 = con.prepareStatement("SELECT * FROM dbo.Logins WHERE Username=? AND Password=?");
s1.setString(1,loginUsername);
s1.setString(2, loginPassword.toString());
ResultSet rs = s1.executeQuery();

int rowCount = rs.last() ? rs.getRow() : 0; //Number of rows available in table for query

if(rowCount>0)
    JOptionPane.showMessageDialog(null, "User Found");
}
else{
    JOptionPane.showMessageDialog(null, "Error");
}

Answer 3

public void Login(String user, String pass) throws ClassNotFoundException, SQLException{ try{ Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver"); MainWindow mw = new MainWindow(); String userName = "<USERNAME>"; String password = "<PASSWORD>"; String url = "<URL>"; Connection con = DriverManager.getConnection(url, userName, password); PreparedStatement s1 = con.prepareStatement("SELECT * FROM dbo.Logins WHERE Username=? AND Password=?"); s1.setString(1,user); s1.setString(2, pass); ResultSet rs = s1.executeQuery(); //int rowCount = rs.last() ? rs.getRow() : 0; //Number of rows System.out.println("Name: " + user + "\nPass: " + pass); if(rs.next()) JOptionPane.showMessageDialog(null, "User Found"); else{ JOptionPane.showMessageDialog(null, "Error"); } con.close();