Resultset To List null [duplicate]

Question

public List<Order> getAllOrdersByCustomerId(int customerId) throws SQLException {
    List<Order> AllOrdersByCustomerId = new ArrayList<>();
    Connection con = null;
    PreparedStatement pstmt = null;
    ResultSet rs = null;


    try {
        String sqlQuery = "SELECT * FROM dbo.Orders WHERE customer_id = ?";
        con = JDBCConnection.getConnection();
        pstmt = con.prepareStatement(sqlQuery);
        pstmt.setInt(1, customerId);
        pstmt.executeUpdate();
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (con != null) {
            JDBCConnection.closeConnection(con);
        }
        if (rs != null) {
            JDBCConnection.closeResultSet(rs);
        }
    }
    return AllOrdersByCustomerId;
}

//Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because "lo" is null

Answer 1

You should use ResultSet to read your Order of SQL query, and add the Order into your List, like below:

public List<Order> getAllOrdersByCustomerId(int customerId) throws SQLException {
    List<Order> allOrdersByCustomerId = new ArrayList<>();
    String sqlQuery = "SELECT * FROM dbo.Orders WHERE customer_id = ?";
    try (Connection con = JDBCConnection.getConnection();
        PreparedStatement pstmt = con.prepareStatement(sqlQuery)) {
        pstmt.setInt(1, customerId);
        try (ResultSet rs = pstmt.executeQuery()) {
            while (rs.next()) {
                Order order = new Order();
                String id = rs.getString("ORDER_ID");
                order.setId(id);

                // get and set your values ...

                allOrdersByCustomerId.add(order);
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return allOrdersByCustomerId;
}