Java对List＜Map＞根据key进行排序、去重、分组
public static void mapListExample() {
Map<String, Object> mapData = new HashMap<String, Object>() {{
put("name", "xiaoyi");
put("age", "28");
put("sex", "male");
}};
Map<String, Object> mapData2 = new HashMap<String, Object>() {{
put("name", "xiaoer");
put("age", "22");
put("sex", "male");
}};
Map<String, Object> mapData3 = new HashMap<String, Object>() {{
put("name", "xiaosan");
put("age", "23");
put("sex", "female");
}};
Map<String, Object> mapData4 = new HashMap<String, Object>() {{
put("name", "xiaoliu");
put("age", "20");
put("sex", "male");
}};
Map<String, Object> mapData5 = new HashMap<String, Object>() {{
put("name", "yanzi");
put("age", "20");
put("sex", "female");
}};
List<Map<String, Object>> mapList = Arrays.asList(mapData, mapData2, mapData3, mapData4, mapData5);
Collections.sort(mapList, new Comparator<Map<String, Object>>() {
@Override
public int compare(Map<String, Object> o1, Map<String, Object> o2) {
return o1.get("name").toString().compareTo(o2.get("name").toString());
}
});
System.out.println(mapList);
mapList.sort(Comparator.comparing(item->item.get("name").toString()));
mapList.sort(Comparator.comparingInt(item->Integer.valueOf(item.get("age").toString())));
System.out.println("根据年龄进行排序======>"+mapList);
//List<Map> 按某个key去重（重要记忆）
ArrayList<Map<String, Object>> mapArrayList = mapList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() ->
new TreeSet<>(Comparator.comparing(item -> item.get("age").toString()))), ArrayList::new));
System.out.println("按某个key去重======>"+mapArrayList);
System.out.println("=========================================================");
//List<Map> groupBy按某个key分组（重要记忆）
//Collector<Map<String, Object>, ?, Map<Object, List<Map<String, Object>>>> age = (item -> ("age"));
Map<String, List<Map<String, Object>>> groupMap = mapList.stream().collect(Collectors.groupingBy(item -> item.get("age").toString()));
System.out.println("groupBy按某个key分组====>"+groupMap);
List<Map<String, Object>> collectList = new ArrayList<>();
for (Map.Entry<String,List<Map<String, Object>>> entry : groupMap.entrySet()){
List<Map<String, Object>> value = entry.getValue();
Map<String, Object> oneMap = value.get(0);
Integer ageAdd = 0;
if (value.size() > 0){
for (Map<String, Object> objectMap : value) {
ageAdd += Integer.valueOf(objectMap.get("age").toString());
}
oneMap.put("age",ageAdd);
collectList.add(oneMap);
}else{
collectList.add(oneMap);
}
}
System.out.println("相同key的年龄相加=======>"+collectList);
}