Dynamic variable key to Nested Java HashMap

Question

I'm new to java.

I need to get the HashMap value from Nested HashMap using its key path and the key is a dynamic variable.

For example the HashMap is

{data={
        "owner" : {
            "id" : 34,
            "firstName" : "John",
            "lastName" : "Smith",
            "owner" : {
                "id" : 44,
                "firstName" : "Henrick",
                "lastName" : "kane"
            },
        },
        "fname" : "sahal",
        "lname" : "kn",
    }
}

And I get the keys like data.owner.owner.id or data.owner.id or fname . So the length of the key path can be any number. above example it is 4 , 3 and 1 . It can be 5, 6, or 7 any. Keys are dynamic so i can't predict how many length to reach the last key value.

Is there a way I can dynamically pull the HashMap value, list like below myHashMaoVariable.get("data.owner.owner.id");

Now what i'm splitting the key data.owner.id to a list and checking
if key[0] > 1 and myHashMaoVariable.containsKey(key[0]), if key[1] > 1 and myHashMaoVariable.get(key[0]).containsKey(key[1]), if key[2] > 1 and myHashMaoVariable.get(key[0]).get(key[1]).containsKey(key[1]), ans so on till key length 5.

Is there a better way to do it to support n number of key path length ? Also there is no depth to the nested map. It is also dynamic.

Answer 1

Supposing you have a top-level map:

Map<String, Object> rootMap = ...//obtain map

You can define a method that reads values up to a certain level dynamically:

static Object readKeyValue(String keyPath, Map<String, Object> root) {

    String[] keys = keyPath.split("\\.");
    Object value = root.get(keys[0]);
    for (int i = 1; i < keys.length; i++) {
        if (i == keys.length - 1) {
            return ((Map<String, Object>) value).get(keys[i]);
        } else {
            value = ((Map<String, Object>) value).get(keys[i]);
        }
    }

    return value;
}

With such a method, you can just invoke it with:

Object value = readKeyValue("data.owner.owner.id", rootMap);

Tested with the following main method:

public static void main(String[] args) {

    Map<String, Object> rootMap = new HashMap<>(), data = new HashMap<>(), owner1 = new HashMap<>(),
            owner2 = new HashMap<>();

    rootMap.put("data", data);
    data.put("owner", owner1);
    owner1.put("owner", owner2);
    owner2.put("firstName", "something");

    System.out.println(rootMap);
    System.out.println(readKeyValue("data.owner.owner.firstName", rootMap));
}

And the following output was produced:

{data={owner={owner={firstName=something}}}}
something