在这种情况下我应该如何使用流

Question

I am new using stream in java and would like to know if there exists a way to optimize this code. I am confused when I should use map or filter in this situation

public Active get(List<Person> personList){
        Active a = null;
        for(Person person:personList){
            if(person.getActives() != null && !person.getActives().isEmpty()){
                for(Active active: person.getActives()){
                    if(active.getStatus().equals(SOME_VALUE)){
                        if (a == null || a.getDueDate().isAfter(active.getDueDate())) {
                            a = active;
                        }
                    }
                }
            }
        }
        return a;
}

Answer 1

  Active a = personList.stream()
         .filter(person -> person.getActives() != null && !person.getActives().isEmpty()
         .flatMap(person -> person.getActivities())
         .filter(activity -> active.getStatus().equals(SOME_VALUE))
         .reduce(null, (pos_a, activity) -> 
           (pos_a == null || a.getDueDate().isAfter(active.getDueDate()))? activity: pos_a)
    return a;

This will get all the Persons that have Activities, stream all the Activity's (flatMap) and filter those on their status and then reduce the list keeping the oldest one