public boolean query(username, password) throws SQLException {
    String dbName;
    String password;
    stmt = dbConnection().prepareStatement("SELECT * FROM customers WHERE Name ='" + username + "' AND Password='" + password + "' ; ");
    while (rs.next()) {
        dbName = rs.getString("Name");
        dbPassword = rs.getString("Password");
     }
     if(dbName.equals(username)&& dbPassword.equals(password)){
        return true;
     }
     else {
        return false;
     }
}

------------------------------------------------------

User user = new User();
DbHandler db = new DbHandler();
user.setName("Johnny");
user.setPassword("pölpungsprut");

if (db.query(user.getName(), user.getPassword())) {
    System.out.println("Welcome!");
}
else {
    System.out.println("sod off, wanker.");
}