java_set

set为无序集合类， 利用Collections.sort升序排列

Set set = new HashSet();

for (int i = 0; i < fogList.size(); i++) {
set.add(fogList.get(i).get("HAPP_DATE"));
}
ArrayList<String> listSet = new ArrayList<String>(); 
listSet.addAll(set);
Collections.sort(listSet);