购物时将商品保存到session
String goodIds = request.getParameter("item");

Map<String, Integer> linkMap = (Map<String, Integer>)session.getAttribute("orderData");
if(linkMap == null){
linkMap = new LinkedHashMap<String, Integer>();
}
if(StringUtils.isNotBlank(goodIds)){
String numStr = request.getParameter("num");//商品数量
if(!StringUtils.isNumeric(numStr)){
numStr = "1";
}
int numInt = Integer.parseInt(numStr);
if(numInt < 1){
numInt = 1;
}

linkMap.put(goodIds, Integer.valueOf(numInt));
request.getSession().setAttribute("orderData", linkMap);
}

Set<String> arrIds = linkMap.keySet();


//循环
for (String id : arrIds) {
if (StringUtils.isBlank(id))
continue;
//获取商品id
String id= id;
//获取商品数量
int num= linkMap.get(id);
}