1、JDK1.8之前：

假設(shè)有實(shí)體類User，里面有字段id，我們將相同id的User進(jìn)行分組，并存放在Map中。（例子不是很恰當(dāng)，但很能說(shuō)明問(wèn)題）

public static void main(String[] args) { List<User> list = new ArrayList<>(); list.add(new User(1, 1)); list.add(new User(1, 2)); list.add(new User(2, 1)); list.add(new User(2, 3)); list.add(new User(2, 2)); list.add(new User(3, 1)); Map<Integer, List<User>> map = new HashMap<>(); for(User user : list){ if(map.containsKey(user.getId())){//map中存在此id，將數(shù)據(jù)存放當(dāng)前key的map中 map.get(user.getId()).add(user); }else{//map中不存在，新建key，用來(lái)存放數(shù)據(jù) List<User> tmpList = new ArrayList<>(); tmpList.add(user); map.put(user.getId(), tmpList); } } System.out.println(map.toString()); }

執(zhí)行結(jié)果：

可以看到達(dá)到了了我們的目的

2、JDK1.8 新特性實(shí)現(xiàn)

Map<Integer, List<User>> map = list.stream().collect(Collectors.groupingBy(User::getId));

附上

List<Map<String, Object>>>分組List<Map<String, Object>>> list = new ArrayList<>();Map<Long, List<Map<String, Object>>> contractIdMap = list.stream().collect(Collectors.groupingBy(m -> (Long.parseLong(m.get('contractId').toString()))));Map<Long, List<Map<String, Object>>> nameMap = list.stream().collect(Collectors.groupingBy(m -> (m.get('name').toString())));

補(bǔ)充知識(shí)：java中對(duì)list的數(shù)據(jù)按照某個(gè)屬性進(jìn)行分組，拆分成多個(gè)list

我就廢話不多說(shuō)了，大家還是直接看代碼吧~

/*** 按照List<Map<String,Object>>里面map的某個(gè)value重新封裝成多個(gè)不同的list, 原始數(shù)據(jù)類型List<Map* <String,Object>>, 轉(zhuǎn)換后數(shù)據(jù)類型Map<String,List<Map<String,Object>>>** @param list* @param oneMapKey* @return*/private static Map<String, Object> change(List<Map<String, Object>> list, String oneMapKey) {Map<String, Object> resultMap = new HashMap<String, Object>();Set setTmp = new HashSet();for (Map<String, Object> tmp : list) {setTmp.add(tmp.get(oneMapKey));}Iterator it = setTmp.iterator();while (it.hasNext()) {String oneSetTmpStr = (String) it.next();List<Map<String, Object>> oneSetTmpList = new ArrayList<Map<String, Object>>();for (Map<String, Object> tmp : list) {String oneMapValueStr = (String) tmp.get(oneMapKey);if (oneMapValueStr.equals(oneSetTmpStr)) {oneSetTmpList.add(tmp);}}resultMap.put(oneSetTmpStr, oneSetTmpList);}return resultMap;}

以上這篇Java 將List中的實(shí)體類按照某個(gè)字段進(jìn)行分組并存放至Map中操作就是小編分享給大家的全部?jī)?nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持好吧啦網(wǎng)。