This should do it.

Map<String, Object> treeMap = mapper.readValue(json, Map.class);

List<String> keys  = Lists.newArrayList();
List<String> result = findKeys(treeMap, keys);
System.out.println(result);

private List<String> findKeys(Map<String, Object> treeMap , List<String> keys) {
    treeMap.forEach((key, value) -> {
      if (value instanceof LinkedHashMap) {
        Map<String, Object> map = (LinkedHashMap) value;
        findKeys(map, keys);
      }
      keys.add(key);
    });

    return keys;
  }

This will print out result as

[required, requiredMsg, choices, exc, a, b, c, required, textbox, d, choiceSettings, type, Settings]

Here is the solution by "Josson & Jossons". I list 2 more examples with condition filtering.

https://github.com/octomix/josson

implementation 'com.octomix.josson:josson:1.3.22'

---------------------------------------------

Josson josson = Josson.fromJsonString(
    "[" +
    "  {" +
    "    \"item\": {" +
    "      \"type\": \"uri\", \"value\": \"http://www.wikidata.org/entity/Q42442324\"" +
    "    }," +
    "    \"prop\": {" +
    "      \"type\": \"uri\", \"value\": \"http://www.wikidata.org/prop/direct/P21\"" +
    "    }," +
    "    \"itemLabel\": {" +
    "      \"xml:lang\": \"en\", \"type\": \"literal\", \"value\": \"Kiisu Miisu\"" +
    "    }" +
    "  }," +
    "  {" +
    "    \"item\": {" +
    "      \"type\": \"uri\", \"value\": \"http://www.wikidata.org/entity/Q43260736\"" +
    "    }," +
    "    \"prop\": {" +
    "      \"type\": \"uri\", \"value\": \"http://www.wikidata.org/prop/direct/P21\"" +
    "    }," +
    "    \"itemLabel\": {" +
    "      \"xml:lang\": \"en\", \"type\": \"literal\", \"value\": \"Paddles\"" +
    "    }" +
    "  }" +
    "]");

JsonNode node = josson.getNode("*.value");
System.out.println("1.\n" + node.toPrettyString());

node = josson.getNode("~'^item.*'.value");
System.out.println("2.\n" + node.toPrettyString());

node = josson.getNode("*[value.type='uri']*.value");
System.out.println("3.\n" + node.toPrettyString());

Output:

1.
[ "http://www.wikidata.org/entity/Q42442324", "http://www.wikidata.org/prop/direct/P21", "Kiisu Miisu", "http://www.wikidata.org/entity/Q43260736", "http://www.wikidata.org/prop/direct/P21", "Paddles" ]
2.
[ "http://www.wikidata.org/entity/Q42442324", "Kiisu Miisu", "http://www.wikidata.org/entity/Q43260736", "Paddles" ]
3.
[ "http://www.wikidata.org/entity/Q42442324", "http://www.wikidata.org/prop/direct/P21", "http://www.wikidata.org/entity/Q43260736", "http://www.wikidata.org/prop/direct/P21" ]

This answer applies to Jackson versions prior to 2+ (originally written for 1.8). See @SupunSameera's answer for a version that works with newer versions of Jackson.

The JSON terms for "node name" is "key." Since JsonNode#iterator() does not include keys, you need to iterate differently:

Copyfor (Map.Entry<String, JsonNode> elt : rootNode.fields())
{
    if ("foo".equals(elt.getKey()))
    {
        // bar
    }
}

If you only need to see the keys, you can simplify things a bit with JsonNode#fieldNames():

Copyfor (String key : rootNode.fieldNames())
{
    if ("foo".equals(key))
    {
        // bar
    }
}

And if you just want to find the node with key "foo", you can access it directly. This will yield better performance (constant-time lookup) and cleaner/clearer code than using a loop:

CopyJsonNode foo = rootNode.get("foo");
if (foo != null)
{
    // frob that widget
}

I think you are not bound to the has() method.

You can convert the json to a map and then find the node recursively

    ObjectMapper mapper = new ObjectMapper();
    Map<String, Object> map = mapper.readValue( body, Map.class );

    ArrayList<Object> container = new ArrayList<>();
    boolean value = find( map, "id", container );

    if( value )
    {
        System.out.println( container );
    }

The recursive method should visit all the nodes and return soon as node is found

private static boolean find( Map<String, Object> map, String search, ArrayList<Object> container )
    {
        int i = 0;
        for( String s : map.keySet() )
        {
            i++;
            if( s.equals( search ) )
            {
                container.add( map.get( s ) );
                return true;
            }
            if( map.get( s ) instanceof Map )
            {
                boolean found = find( (Map<String, Object>) map.get( s ), search, container );
                if( i == map.size() || found )
                {
                    return found;
                }
            }
        }
        return false;
    }

I have edited the code to get the value also. hope this helps. I strongly suggest you to do more research on yourself before looking for help from the community.