How to know if a key exists in inner map using java?

In the below map how do I know if key3 exists without going through a brute force for-loop and check inside every inner map. Given that all keys will be unique do we have any library functions doing it?

"map": {
        "key1": "value1",
        "innerMap": {
          "key2": "value2",
          "innerMap2": {
            "key3": "value3"
          }
        }
      }

Assuming that your picture describes a Map, then a "brute-force" tree traversal is your best option.

There is no standard Java SE API for searching nested maps.

@f1sh mentioned the possibility of doing a string search ... assuming that the map is actually JSON. There are some important caveats:

1. String searching a JSON string (or the result of calling Map.toString()) is potentially fragile. For example, .contains("\"key3\":") would give false matches if a value in the map contained that search string.

2. Rendering a Map to JSON (or whatever) to do a string search will be more expensive than doing the search.

3. A String.contains search potentially entails looking at every character in the serialization. That's just as "brute-force" as a tree traversal.

The only alternative that I can think of that is not "brute-force" is to create an auxiliary data structure; e.g. HashSet of all (unique) keys in the map tree. Once created, the set can be queried in O(1) ... but creating it is O(N) where N is the number of (non-distinct!) keys in the tree.

Finally, the map tree traversal could be a recursive method rather than (just) a mess of for loops.