使用JAVA8 lambda表达式 对List集合去重及分组

users.stream().forEach(user -> {
    System.out.print(+user.getId()+"--"+user.getName()+"   ");
});

获取实体类对象中某一个字段转为List

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

根据单个字段字段去除重复

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

根据多个字段去除重复

List userList = users.stream() .collect(
        Collectors.collectingAndThen(
                Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(user -> user.getName()+";"+user.getId()))), ArrayList::new));
List去重两个相同的实体类对象或者相同的单个对象字段

List classNameList = new ArrayList(new HashSet(userList));

根据某个字段分组

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