同一组数据分组 需求：一个 list 里可能会有出现一个用户多条数据的情况。要把多条用户数据合并成一条。

    public static void main(String[] args) {
        List<User> users = Arrays.asList(
                new User(1, "liu big big", "123456789"),
                new User(2, "liu big big", "987654321"),
                new User(3, "su xiao xiao", "55555555")
        );
        Map<String, Set<User>> map = new HashMap<>();

        for (User user : users) {
            Set<User> userSet = map.get(user.getName());
            if (null == userSet) {
                userSet = new HashSet<>();
                userSet.add(user);
                map.put(user.getName(), userSet);
            } else {
                userSet.add(user);
            }
        }

        Set<String> keySet= map.keySet();
        Iterator<String> it = keySet.iterator();
        while(it.hasNext()){
            String key = it.next();
            Set<User> user = map.get(key);
            System.out.println(user.toString());
        }
    }

}



class User {

    public User(Integer id, String name, String phone) {
        this.id = id;
        this.name = name;
        this.phone = phone;
    }

    private Integer id;

    private String name;

    private String phone;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }
}