ReckoningServlet代码如下：
	package servlet.user;
	import java.io.IOException;
	import java.sql.Connection;
	import java.sql.ResultSet;
	import java.sql.Statement;
	import java.util.ArrayList;
	import java.util.Iterator;
	import javax.servlet.RequestDispatcher;
	import javax.servlet.ServletException;
	import javax.servlet.http.HttpServlet;
	import javax.servlet.http.HttpServletRequest;
	import javax.servlet.http.HttpServletResponse;
	import javax.servlet.http.HttpSession;
	import dao.DBConnection;
	import bean.Cart;
	import bean.CartItem;
	public class ReckoningServlet extends HttpServlet {
		public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
			HttpSession session = request.getSession();
			Cart cart = (Cart) session.getAttribute("cart");
			if (cart == null || cart.getCart().size()==0) {
				request.setAttribute("null", "1");
			} else {
				ArrayList login = (ArrayList) session.getAttribute("login");
				String userId = (String) login.get(0);
				DBOperation dbo=new DBOperation();
				ArrayList<CartItem> al = cart.getCart();
				Iterator<CartItem> it = al.iterator();
				String bookId = "";
				int bookQuantity = 0;
				String SQL1 = "";
				String SQL2 = "";
				String SQL3 = "";
				String SQL4 = "";
				while(it.hasNext()){
				CartItem cartItem = it.next();
				bookId = cartItem.getId();
				bookQuantity = cartItem.getQuantity();
				SQL1 = "update books set storage=storage-"+bookQuantity+" where id = 
				"+bookId+"";
				dbo.insertDeleteUpdate(SQL1);
				SQL2 = "insert into orders(userid,bookid,booksum,times) values
	 			("+userId+","+bookId+","+bookQuantity+",Getdate())";
				dbo.insertDeleteUpdate(SQL2);
				SQL3 = "select * from rank where bookid = "+bookId+"";
				if(dbo.queryReturnboolean(SQL3)){
					SQL4 = "update rank set quantity=quantity+"+bookQuantity+" where 
					bookid="+bookId+"";
					dbo.insertDeleteUpdate(SQL4);
				}else{
					SQL4 = "insert into rank(bookid,quantity) values("+bookId+",
					"+bookQuantity+")";
					dbo.insertDeleteUpdate(SQL4);
				}	
			}
			request.setAttribute("ok", "1");
			session.removeAttribute("cart");
		}
		RequestDispatcher rd = request.getRequestDispatcher("/user/cart.jsp");
			rd.forward(request, response);
		}
		public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
			doGet(request, response);
		}
	}