前几天面试的时候被面试官出了这样的一道题：

有一个Map为Map<String,Object>，其中的Object类有三种类型：
1.Person类；
2.List<person>或者List<List<person>>或者List<List<List<person>>>等等等等…
3.Map<String,Object>(此Map和题中的Map一样内部有三种类型)；
(其中的Person已经指定好，不用自己写)

现将这个Map中包涵的所有的Person类对象都打印出来

面试的时候想到用instanceof和递归解决，但只写出来一半，现在将完整题解写一下

Person类

public class Person{
    private String name;

    public Person(String name) {
        this.name = name;
    }
    
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                '}';
    }
}

用于生成包涵三种类型的Map的工具类

public class MapCreate {
    public static Map<String, Object> map = new HashMap<>();

    static {
        setMap();
    }

    private static void insertList(Map<String, Object> map, String... name) {
        ArrayList<Person> people = new ArrayList<>();
        people.add(new Person(name[0]));
        people.add(new Person(name[1]));
        ArrayList<Person> peopleIn = new ArrayList<>();
        peopleIn.add(new Person(name[2]));
        peopleIn.add(new Person(name[3]));
        ArrayList<Person> peopleIn2 = new ArrayList<>();
        peopleIn2.add(new Person(name[4]));
        peopleIn2.add(new Person(name[5]));
        ArrayList<List<Person>> listInList = new ArrayList<>();
        ArrayList<List<Person>> listInList2 = new ArrayList<>();
        listInList.add(peopleIn);
        listInList2.add(peopleIn2);
        ArrayList<List<List<Person>>> listInListInList = new ArrayList<>();
        listInListInList.add(listInList2);
        map.put("list", people);
        map.put("listInList", listInList);
        map.put("listInListInList", listInListInList);
    }

    private static void setMap() {
        map.put("zhang", new Person("张三"));
        map.put("li", new Person("李四"));
        map.put("wang", new Person("王五"));

        HashMap<String, Object> innerMap = new HashMap<>();
        innerMap.put("a", new Person("AAA"));
        innerMap.put("b", new Person("BBB"));
        innerMap.put("c", new Person("CCC"));
        innerMap.put("map", new HashMap<String, Object>());
        insertList(innerMap, "mapListPerson1", "mapListPerson2", "mapListInListPerson1", "mapListInListPerson2", "mapListInListInListPerson1", "mapListInListInListPerson2");
        map.put("map", innerMap);

        insertList(map, "listPerson1", "listPerson2", "listInListPerson1", "listInListPerson2", "listInListInListPerson1", "listInListInListPerson2");
    }
}

利用递归和instanceof实现

public class Main {

    private static List<Person> personList = new ArrayList<>();

    public static void main(String[] args) {
        searchMap(MapCreate.map);
        for (Person person : personList) {
            System.out.println(person);
        }
    }

    private static void searchMap(Map<String,Object> map){
        Collection<Object> values = map.values();
        for (Object value : values) {
            if(value instanceof Person){
                personList.add((Person) value);
            }else if(value instanceof Map){
                searchMap((Map<String, Object>) value);
            }else if(value instanceof List){
                searchList((List<Object>) value);
            }
        }
    }

    private static void searchList(List<Object> list){
        for (Object o : list) {
            if(o instanceof Person){
                personList.add((Person) o);
            }else if(o instanceof List){
                searchList((List<Object>) o);
            }
        }
    }
}