PSQLException：ResultSet放置不正确，也许您需要调用下一个

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;
}

我正在使用此代码对用户进行身份验证。用户名和密码是从request参数中提取的，并传递到此方法进行身份验证。但是它抛出：

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.

请咨询。