合并一个List中相同元素，并汇总指定属性

http://hsj69106.blog.51cto.com/blog/1017401/489611

public static void mergeList(List list) {
    HashMap map = new HashMap();
    for (Bean bean : list) {
        if (map.containsKey(bean.getType())) {
            bean.setQuantity(map.get(bean.getType()).getQuantity() + bean.getQuantity());
        }
        map.put(bean.getType(), bean);
    }
    list.clear();
    list.addAll(map.values());
}