iterate, find and update value in nested Map<String, ?>

Question

I have a YML file, which I parse to Map using yamlBeans library. I don't know how deep the nested map goes. for example:

• key1:
  • key2: value1
  • key3:
    • key4: value2
    • key5: value3

I need to find a specific value in this map, update it, and write the map back to YML file (which I know how to do).

This is my code for updating the value, and it's working. However, this is only iterating twice through the nested map, and I need it to iterate it for as long as needed:

    static void updateYmlContent(Map<String, ?> ymlMap, String value, String... keys) {
    boolean found = false;
    for (Map.Entry entry : ymlMap.entrySet()) {
        if (entry.getKey().equals(keys[0])) {
            found = true;
            for (Map.Entry subEntry : ((Map<?, ?>) entry.getValue()).entrySet()) {
                if (subEntry.getKey().equals(keys[1])) {
                    subEntry.setValue(value);
                    break;
                } else {
                    throwKeyNotFoundException(keys[1]);
                }
            }
            break;
        }
    }
    if (!found) {
        throwKeyNotFoundException(keys[0]);
    }
}

Answer 1

Use recursion and a depth counter to drop through each level of the map. I didn't compile this, so it probably needs a little tweaking, but here's the basic idea:

static void updateYmlContent(Map<String, ?> ymlMap, String value, String... keys) {
    int depth = 0;
    findAndReplaceContent(ymlMap, value, keys, depth);
}

static void findAndReplaceContent(Map map, .......) {
  if (map.containsKey(keys[depth]))
  {
    if (depth == keys.length - 1)
    {
      // found it
      map.put(keys[depth], value);
      // done
    }
    else
    {
      findAndReplaceContent(map.get(keys[depth]), value, keys, depth+1);
    }
  }
  else
  {
    // throw key not found
  }
}