Java SQL Check if username already exists

Question

I am trying to check if the username already exists in the table: The database also has the field set to unique The method will return a boolean stating if the username already exists or not. The part of my code that sets the usernameExists var to true never runs even if the usernames are the same.

 public static boolean CheckUsernameExists(String username)
{
    boolean usernameExists = false;

    try
    {

        Class.forName("com.mysql.jdbc.Driver");
        Connection connection = DriverManager.getConnection(urlDB, usernameDB, passwordDB);

        PreparedStatement st = connection.prepareStatement("select * from Members order by username desc");
        ResultSet r1=st.executeQuery();
        String usernameCounter;
         if(r1.next()) 
         {
           usernameCounter =  r1.getString("username");
           if(usernameCounter == username) //this part does not happen even if it should
           {
               System.out.println("It already exists");
              usernameExists = true;
           }
         }


     }

     catch (SQLException e) 
     {
        System.out.println("SQL Exception: "+ e.toString());
     } 
     catch (ClassNotFoundException cE) 
     {
        System.out.println("Class Not Found Exception: "+ cE.toString());
     }

 return usernameExists;
 }

IF you can help in anyway I would be thankful!

you could just query for that specific username, and if anything at all is returned, then it's there. otherwise you'd get a soft-fail and no resultset and/or an empty resultset. — SnakeDoc, Jan 24 '14 at 16:42
Did you try adding a debug statement to show what r1.getString("username") was? — James Kingsbery, Jan 24 '14 at 16:52

score 2 · Accepted Answer · edited May 23 '17 at 10:29

2

Use if(usernameCounter.equals(username)). String comparisons are tricky. This has been discussed in detail here.

edited May 23 '17 at 10:29

Community

1
1

answered Jan 24 '14 at 16:39

Sujith Surendranathan

2,569
17
21

score 2 · Answer 2 · answered Jan 24 '14 at 16:48

2

Never compare two String instances using ==, use equals() (== checks for identity, not equality).

You could also directly use the username in the query, rather than taking the username from the query result:

PreparedStatement st = connection.prepareStatement("select * from Members where username = ?");
st.setString(1, username);
ResultSet r1=st.executeQuery();
if(r1.next()) {
  usernameExists = true;
}

answered Jan 24 '14 at 16:48

EmirCalabuch

4,756
1
25
20

The problem is that some names are treated the same. For example: emircal1234 this name exists. New name: emir1111111111111111 the name is used because it has an *emir* in it. – Љубинко Стојановић - Смртник Jan 27 '22 at 09:04

M21B8 · Answer 3 · 2014-01-24T16:56:21.140

As everyone has pointed out, you need to use .equals when you compare strings. however for your usage, I would recommend using .equalsIgnoreCase, as you probably want it to treat "MSmith" and "msmith" as the same.

Also, a much more efficient way to perform this check would be to select the row on the table

PreparedStatement st = connection.prepareStatement("select * from Members username=?");
st.setString(1,username);

Then, if you get a row, you know the username is already used. If you don't get a row or you get a RowNotFoundException, then you can treat that as "the username has not been used". Again, you would need to be careful with the case of the input when doing the check.

score 0 · Answer 4 · answered Jan 24 '14 at 16:43

0

Your problem is usernameCounter == username. You are comparing objects where instead I think you want to be comparing strings.

try usernamecounter.equals(username)

answered Jan 24 '14 at 16:43

user3229382

81
1
4

Java SQL Check if username already exists

4 Answers4