我於
List dataList = dataDao.getAll();
String.valueOf(dataList.get(0).getStime())

撈出來的資料如下
=dataList:Thu Jun 13 10:28:11 CST 2019

我想在Action裡面，把 dataList 跟 Data data 的資料都改成 YYYY-MM-DD
並且dataList得去除重複的日期

HashMap<String, Integer> map = new HashMap

for(Data data: dataList){
Date Stime = data.getStime();
String str = String.valueOf(Stime);
map.put(str, 0);
}

我想試著改Data.java 裡面的格式，但我想不到方法

@Table(name = "Data")
@XmlRootElement
@NamedQueries({
@NamedQuery(name = "Data.findAll", query = "SELECT e FROM Data e"),
@NamedQuery(name = "Data.findById", query = "SELECT e FROM Data e WHERE e.id = :id"),
@NamedQuery(name = "Data.findByStime", query = "SELECT e FROM Data e WHERE e.stime = :stime"),

肯請各位賜教了