初始代码
public Map<String,List<RgwstBean>> getMap(List<RgwstBean> lists){
Map<String,List<RgwstBean>> map = new TreeMap<String,List<RgwstBean>>();
if(lists==null) {
return map;
}
for(RgwstBean rb :lists) {
String newdate = rb.getDatetime();
if(map.containsKey(newdate)) {
map.get(newdate).add(rb);
}else {
List<RgwstBean> newlist2 = new ArrayList<RgwstBean>();
newlist2.add(rb);
map.put(newdate, newlist2);
}
}
return map;
}
lambda语法
public Map<String,List<RgwstBean>> getMap(List<RgwstBean> lists){
//groupingBy无排序
Map<String,List<RgwstBean>> map = lists.stream().collect(Collectors.groupingBy(RgwstBean::getDatetime));
Map<String,List<RgwstBean>> sortmap = new TreeMap<>();
//Map<String,List<RgwstBean>> sortmap = new TreeMap<>((o1,o2)->o2.compareTo(o1));//倒序
map.entrySet()
.stream()
.forEach(x->sortmap.put(x.getKey(),x.getValue()));
return sortmap;
}