PSQLException: ResultSet not positioned properly, perhaps you need to call next

问题

public UserBean authenticate(String username,String password){
    PostGresDAO pg=new PostGresDAO();   //creates new connection
    Connection conn=pg.getConnecion();  //return connection object
    PreparedStatement ps;
    ResultSet rs;
    String query="select password,name from scg_users where username=?";
    UserBean ub=null;
    boolean authenticated=false;
    try{
        ps=conn.prepareStatement(query);
        ps.setString(1, username);
        rs=ps.executeQuery();

        if(rs!=null){

            authenticated=password.equals(rs.getString(1));  //exception raised here
            if(authenticated){
                ub=new UserBean();
                ub.setUser(rs.getString(2));
                ub.setUsername(username);
            }
        }
    }
    catch(SQLException e){
        e.printStackTrace();
    }
    return ub;
}

I am using this code for authenticating a user. The username and password are extracted from the request parameter and passed onto this method for authentication. But it throws a:

org.postgresql.util.PSQLException: ResultSet not positioned properly, perhaps you need to call next.

Please advice.

回答1:

The error is telling you exactly what's wrong - you're not calling next() on your ResultSet to get to the first row of the results.

This line:

if(rs!=null)

is pointless as far as I know; I don't believe executeQuery will ever return null. If there's a problem in your query, an exception will be thrown. If there are no results, it will return an empty result set. To see if there's a row, you should call next() and check the return value:

if (rs.next())

Additionally:

Catching an exception and just printing the stack trace without rethrowing is almost always the wrong approach
Your code suggests that you're storing passwords in plain text. Please don't. Really, really don't.

回答2:

Because I got the message even when I called next() on resultSet I'll tell my solution.

The solution is NOT to call resultSet.get* on your resultSet if it's empty. So do a check if(resultSet.next()){ ...

回答3:

Instead of

if(rs!=null)

You need to check for

if(rs.next())

This will return the first row, if there are any matching rows.

来源：https://stackoverflow.com/questions/12103915/psqlexception-resultset-not-positioned-properly-perhaps-you-need-to-call-next

标签

java

postgresql

postgresql-9.1