json - Retrieve name of fields of a JSONObject - Java

I have to retrieve all name of fields of JSONObjectin Java.

For example, this is a JSON:

{
"name" : {
        "first" : "John",
        "last" : "McCarthy"
    },
"birth" : ISODate("1927-09-04T04:00:00.000Z"),
"death" : ISODate("2011-12-24T05:00:00.000Z"),
"contribs" : [ 

        "Lisp", 
        "Artificial Intelligence", 
        "ALGOL"
    ]
}

This JSON object is just an example, I can't know what a JSONObject contains since I import it. I don't have any information about the name of fields to use Gson/Jackson to deserialization.

Suppose I have a JSONObject myDocJson that contains the previous JSON Object, I use an iterator:

Iterator keys = myDocJson.keySet().iterator();
while(keys.hasNext()) {
System.out.println(keys.next());
}

And as a result I get:

name

birth
death
contribs

But for example I don't have name.first and name.last. So this iterator does not work with innested Object.