Can anyone tell me what is wrong with my code here, and what is the best approach to do the same thing?

I'm trying to connect to a database and retrieve a list of unprocessed orders, recreate the order object which takes as parameters, a customer object, a product object, and an integer (unity).

These methods exist in my connection class:

public Map<String, Cliente> loadCustomerList() throws SQLException {
    conexion = DriverManager.getConnection(this.url, this.user, this.password);
    Map<String, Cliente> listaClientes = new HashMap<>();
    query = "SELECT * FROM cliente";
    st = conexion.prepareStatement(query);
    rs = st.executeQuery();
    while (rs.next()) {
        String dni = rs.getString(1);
        String nombre = rs.getString(2);
        String apellidos = rs.getString(3);
        int descuento = rs.getInt(4);

        listaClientes.put(dni, new Cliente(dni, nombre, apellidos, descuento));
    }

    //conexion.close();
    return lista Clientes;
}

public List<Item> loadItemList() throws SQLException {
    conexion = DriverManager.getConnection(this.url, this.user, this.password);
    List<Item> listaItems = new ArrayList<>();
    query = "SELECT * FROM item;";
    st = conexion.prepareStatement(query);
    rs = st.executeQuery();
    while (rs.next()) {
        String nombre = rs.getString(1);
        double precio = rs.getDouble(2);
        int existencias = rs.getInt(3);

        listaItems.add(new Item(nombre, precio, existencias));
    }

    //conexion.close();
    return listaItems;
}

public Cliente findClient(String dni) throws SQLException {
    Cliente cliente = null;
    for (Map.Entry<String, Cliente> entry : loadCustomerList().entrySet()) {
        if(entry.getKey().equals(dni)) {
            cliente = entry.getValue();
        }
    }
    return cliente;
}
    
public Producto findItem(String nombreProduco) throws SQLException {
    Producto producto = null;
    for(Producto item : loadListItems()) {
        if(item.getNombre().equals(nombreProduco)) {
            producto = item;
        }
    }
    return producto;
}

public List<Pedido> loadOrderList() throws SQLException {
    conexion = DriverManager.getConnection(this.url, this.user, this.password);
    List<Pedido> listaPedidos = new ArrayList<>();
    Cliente cliente =null;
    Producto producto =null;
    query = "SELECT * FROM pedido WHERE `Numero Factura` IS NULL";
    st = conexion.prepareStatement(query);
    rs = st.executeQuery();
    while (rs.next()) {
        int unidad = rs.getInt(3);
         producto = findItem(rs.getString(2));
         cliente = findClient(rs.getString(6));
         listaPedidos.add(new Pedido(producto, unidad, cliente));
    }
    
    conexion.close();
    
    return listaPedidos;
}

I want to be able to call the loadOrderList() method in the constructor of the main operation class like this:

public class PruebaComercio {

    private Map<String, Cliente> listaClientes;
    private List<Pedido> listaPedidos;
    private List<Factura> listaFacturas;
    private Almacen almacen;
    private ConnectionMysql connection = new ConnectionMysql();

    public PruebaComercio() throws SQLException {
        this.listaClientes = connection.cargarListaClientes();
        this.listaPedidos = connection.loadOrderList();
        this.listaFacturas = new ArrayList<>();
        this.almacen = new Almacen();
    }

Output:

Exception in thread "main" java.sql.SQLException: After end of result set
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:89)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:63)
    at com.mysql.cj.jdbc.result.ResultSetImpl.checkRowPos(ResultSetImpl.java:532)
    at com.mysql.cj.jdbc.result.ResultSetImpl.getString(ResultSetImpl.java:878)
    at Facturacion.ConnectionMysql.cargarListaPedido(ConnectionMysql.java:166)
    at Facturacion.PruebaComercio.<init>(PruebaComercio.java:23)
    at Facturacion.Main.main(Main.java:25)

Sorry for the use of Spanish here, the project was done in Spanish, I did my best to translate the important things.

CodePudding user response：

loadOrderList calls (indirectly) loadItemList which changes the st and rs fields while rs is still needed in loadOrderList for the next iterations.