Servlet Sessionの仕方

package action;

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import bean.ZaikoBean2;

@WebServlet("/TanaoroshiItiranServlet")
public class TanaoroshiItiranServlet extends HttpServlet {

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {


	List<Integer> zissuList=new ArrayList<>();

	zissuList.add(Integer.parseInt(req.getParameter("foznum")));
	zissuList.add(Integer.parseInt(req.getParameter("tptoznum")));
	zissuList.add(Integer.parseInt(req.getParameter("tomnum")));
	zissuList.add(Integer.parseInt(req.getParameter("letnum")));
	zissuList.add(Integer.parseInt(req.getParameter("oninum")));
	zissuList.add(Integer.parseInt(req.getParameter("picnum")));
	zissuList.add(Integer.parseInt(req.getParameter("chenum")));
	zissuList.add(Integer.parseInt(req.getParameter("ketnum")));
	zissuList.add(Integer.parseInt(req.getParameter("bacnum")));
	zissuList.add(Integer.parseInt(req.getParameter("fiinnum")));
	zissuList.add(Integer.parseInt(req.getParameter("foinnum")));




	String url = "jdbc:oracle:thin:@localhost:1521/XE";
	String sql = "SELECT * FROM ZAIKOTABLE ORDER BY 商品ID";

	List<ZaikoBean2> list = new ArrayList<>();

	try (Connection con = DriverManager.getConnection(url, "SYSTEM", "abc");
			Statement stmt = con.createStatement();
			ResultSet rs = stmt.executeQuery(sql)) {

		int i = 0;
		while (rs.next()) {
			ZaikoBean2 zr = new ZaikoBean2();
			zr.setId(rs.getString("商品ID"));
			zr.setName(rs.getString("商品名"));
			zr.setZaikosu(rs.getString("理論在庫"));

			int riron = rs.getInt("理論在庫");

			int zissu = zissuList.get(i);
			int sai = riron - zissu;

			i++;

			zr.setZissu(zissu);
			zr.setSai(sai);
			list.add(zr);
		}
	} catch (SQLException e) {
		e.printStackTrace();
	}


	req.setAttribute("zaiko2_list", list);

	req.getRequestDispatcher("Tanaoroshiitiran.jsp").forward(req, resp);
}