I need to rename one field in document

Question

Here is the code :

AggregateIterable<Document> result = chatLogCollection.aggregate(Arrays.asList(
            new Document("$match", new Document("displayName", "user")),
            new Document("$group", new Document("_id","$sessionGUID")
                    .append("time", new Document("$first","$ts"))
                    .append("makerID", new Document("$first","$makerID"))),
            new Document("$sort", new Document("time", -1)),
            new Document("$skip", skip),
            new Document("$limit", limit)
    ));

This will generate the below type out put.

{
    "displayName": "test test",
    "_id": "123a54be-4b69-cd49-edb3-9b264fea077b",
    "time": {
        "$date": 1499759619016
    },
    "makerID": "xxxxx"
}

I need to format this to look like this:

{
    "displayName": "test test",
    "sessionID": "123a54be-4b69-cd49-edb3-9b264fea077b",
    "time": {
        "$date": 1499759619016
    },
    "makerID": "xxxxx"
}

That means i need to appear _id as sessionId. Please help me to do that.I am using mongoDB, java and windows 7.