Conversion between List maps

Other useful places are writing

1. List transfer

1. List transfer List<Object.properties>

	public List extractListProperties(List<User> user) {
    
    
		return users.stream().map(User::getId).collect(Collectors.toList());
	} 

2. List Group Map

	public Map groupList(List<User> user) {
    
    
		return user.stream().collect(Collectors.groupingBy(User::getGroupId()));
	}