Comparator.nullsLast 处理空值

		List<User> list1 = new ArrayList();
        User user = new User("1001","abc1","12",12);
        User user1 = new User("1003","abc2","12",13);
        User user2 = new User("1002","abc3","12",15);
        User user3 = new User("1005","abc4","12",10);
        User user4 = new User(null,"abc5","12",10);
        list1.add(user);
        list1.add(user1);
        list1.add(user2);
        list1.add(user3);
        list1.add(user4);
        //对第一个参数进行排序 
        list1.sort(Comparator.comparing(User::getSiteCode,Comparator.nullsLast(Comparator.naturalOrder())));
        list1.forEach(System.out::println);
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//控制台输出
User(siteCode=1001, userName=abc1, password=12, age=12)
User(siteCode=1002, userName=abc3, password=12, age=15)
User(siteCode=1003, userName=abc2, password=12, age=13)
User(siteCode=1005, userName=abc4, password=12, age=10)
User(siteCode=null, userName=abc5, password=12, age=10)
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