JAVA8 lambda表达式

 

1.获取实体类对象中某一个字段转为List

List<Long> userIds = users.stream().map(User::getId).collect(Collectors.toList());

2.根据单个字段字段去除重复

List<User> userList = users.stream() .collect(
        Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(user ->user.getName()))), ArrayList::new)); 

3.根据多个字段去除重复

List<User> userList = users.stream() .collect(
        Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(user -> user.getName()+";"+user.getId()))), ArrayList::new));

4.根据某个字段分组

users.stream().collect(Collectors.groupingBy(User::getName))

 

来源：https://www.cnblogs.com/ynhk/p/11526275.html