public boolean userName_IsValid(String user)
    {
    	Connection con = null;
        Statement stmt = null;
        try {
            DBconnection dbCon = new DBconnection();
            Class.forName(dbCon.getJDBC_DRIVER());

            con = DriverManager.getConnection(dbCon.getDATABASE_URL(),
                    dbCon.getDB_USERNAME(), dbCon.getDB_PASSWORD());
            stmt = con.createStatement();
            ResultSet rs = stmt.executeQuery("Select cst_id From customer Where cst_username='" + user+"'");
            if (rs.next()) {
               
            	return false;
            }
        } catch (SQLException | ClassNotFoundException ex) {
            System.err.println("Caught Exception: " + ex.getMessage());
        } finally {
            try {
                if (stmt != null) {
                    stmt.close();
                }
                if (con != null) {
                    con.close();
                }
            } catch (SQLException ex) {
                System.err.println("Caught Exception: " + ex.getMessage());
            }
        }
        return true;
    	
    	
    }