In my mongoDB book collection I have documents structured as follow : 

/* 0 */
{
  "_id" : ObjectId("50485b89b30f1ea69110ff4c"),

  "publisher" : {
    "$ref" : "boohya",
    "$id" : "foo"
  },
  "displayName" : "Paris Nightlife",
  "catalogDescription" : "Some desc goes here",
  "languageCode" : "en",
  "rating" : 0,
  "status" : "LIVE",
  "thumbnailId" : ObjectId("50485b89b30f1ea69110ff4b"),
  "indexTokens" : ["Nightlife", "Paris"]
}

I perform the following regex query to find all documents having one indexToken starting with "Par" : 

{ "indexTokens" : { "$regex" : "^Par" , "$options" : "i"}}

If I select only the indexTokens field to be returned like this :

{ "indexTokens" : 1}

The resulting DBObject is 

{ "_id" : { "$oid" : "50485b89b30f1ea69110ff4c"} , "indexTokens" : [ "Nightlife" , "Paris"]}

What I would like to get is ONLY the token / tag that matched the regex (I don0t care about retrieving the document at this point, neither do I need all the tags of the matched document)

Is this a case for the new Aggregation Framework relesed under MongoDB v2.2. ?

If yes how do I modify my query so that the actual result would look like :

{ "indexTokens" : ["Paris", "Paradise River", "Parma" , etc ....]}

Bonus question (do you has teh codez) : How do I do it using the Java driver ?

For now my java looks like : 

DBObject query = new BasicDBObject("indexTokens", java.util.regex.Pattern.compile("^"+filter+"", Pattern.CASE_INSENSITIVE));
    BasicDBObject fields = new BasicDBObject("indexTokens",1);
    DBCursor curs = getCollection()
                    .find(query, fields)
                    .sort( new BasicDBObject( "indexTokens" , 1 ))
                    .limit(maxSuggestionCount);

Thx :)

EDIT:

As per your answers I modified my JAVA code as

mongodb aggregation-framework
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