Lambda
排序
1.单字段排序，根据id排序
userList.sort(Comparator.comparing(User::getId));
2.多字段排序，根据id，年龄排序
userList.sort(Comparator.comparing(User::getId).thenComparing(User::getAge));
list转map
Map<Long, User> userMap = userList.stream().collect(Collectors.toMap(User::getId, a -> a,(k1,k2)->k1))
求最小对象 min、max
Comparator comparator = Comparator.comparing(User::getAge);
User user = userList.stream().min(comparator).get();
判断字段为空
stream.filter(x -> x.getDateTime()!=null)
过滤
List userCommonList = userList.stream().filter(a -> !a.getJobNumber().equals(“201901”)).collect(Collectors.toList());
求和
Integer sum = userList.stream().collect(Collectors.summingInt(User::getAge));
去重
List sLists = userList.stream().collect(
Collectors.collectingAndThen(Collectors.toCollection(
() -> new TreeSet<>(Comparator.comparing(c -> c.getAge()))), ArrayList::new));
这种滤重的方法有个缺点，就是获取的list可能每回返回的结果是随机的