public class Goods implements Comparable {

//    初始化各成员变量

private String Id = null;//商品的编号Id

private String name = null;//商品的名称name

private float price = 0.00F;//商品的价格price

private int number = 0;//商品的数量number

public Goods(String Id, String name, float price, int number) {
        this.Id = Id;
        this.name = name;
        this.price = price;
        this.number = number;

}

public String getId() //返回订购商品的编号Id

{
        return this.Id;
    }

public String getName() //返回订购商品的名称name

{
        return this.name;
    }

public float getPrice() //返回订购商品的价格price

{
        return this.price;
    }

public int getNumber() //返回订购商品的数量number

{
        return this.number;
    }

public int compareTo(Object m) {
        // TODO Auto-generated method stub

Goods n = (Goods) m;
        int comRs = Id.compareTo(n.Id);
        return comRs;

}

request.setCharacterEncoding("GBK");
//获取参数信息

String id = request.getParameter("id");
String name = request.getParameter("name");
int number = java.lang.Integer.parseInt(request.getParameter("number"));
float price= java.lang.Float.parseFloat(request.getParameter("price"));

//建立商品对象和ArrayList对象

Goods goods = new Goods(id,name,price,number);
ArrayList ay = null;
//如果session中从未写入过，则将建立的商品对象添加到ArrayList对象当中，并写入 session

if((ArrayList)session.getAttribute("car")==null)
{
    ay = new ArrayList();
    ay.add(goods);
    session.setAttribute("car",ay);
    response.sendRedirect("order_index.jsp");
}
//如果写如过，则将商品对象添加到ArrayList对象当中，并写入 session

else
{
ay=(ArrayList)session.getAttribute("car");
    //如果ArrayList 对象为空，则直接添加到ArrayList对象当中

if(ay.isEmpty())
{
        ay.add(goods);
        session.setAttribute("car",ay);
        response.sendRedirect("order_index.jsp");
    }
    //如果ArrayList 对象不为空，则判断购入商品是否已经存在于车中

else
{
        Iterator it = ay.iterator();
        for(int i = 0;i<ay.size();i++) //下面还有另一种遍历方法

{
            Goods shop = (Goods)it.next();
//如果购入商品已经存在，则打印输入提示信息

if(shop.compareTo(goods)==0)
{
            out.println(" ");
            }
//如果购入商品不存在，则直接将商品添加到ArrayList对象当中，并写入 session

else
            {
            ay.add(goods);
            session.setAttribute("car",ay);
            response.sendRedirect("order_index.jsp");
            }
        }
    }
}
%>

request.setCharacterEncoding("gb2313");
//获取参数信息

String id = request.getParameter("id");
String name = request.getParameter("name");
float price = java.lang.Float.parseFloat(request.getParameter("price"));
int number = java.lang.Integer.parseInt(request.getParameter("number"));
//创建符合条件参数要删除的商品对象

Goods goods = new Goods(id,name,price,number);
//获取session 中存储的ArrayList对象

ArrayList ay = (ArrayList)session.getAttribute("car");
Iterator it = ay.iterator();
//遍历ArrayList对象，并将ArrayList对象中的元素和创建的符合参数条件要删除的商品进行比较

for(int i = ay.size();it.hasNext();i--)
{
    Goods shop = (Goods)it.next();
    
//查询是否有ArrayList对象中的元素与要删除的商品相同

if(shop.compareTo(goods)==0)
{
        int index = ay.indexOf(shop);
        
//如果ArrayList对象已经为空，则跳转

if(ay.isEmpty())
{
            response.sendRedirect("order_index.jsp");
        }
        
//如果ArrayList对象不为空，则从其中移去要与要删除的商品条件相符的元素，并重新写session