Actually, the configuration option takes a WriteConcern in parameter and not a numeric value.
http://api.mongodb.org/java/current/com/mongodb/MongoClientOptions.Builder.html#writeConcern(com.mongodb.WriteConcern)

So I think, I'll create a bunch of option "mapped" on the static values described here: http://api.mongodb.org/java/current/com/mongodb/WriteConcern.html

I'll open a new JIRA for that. And then check if I'll implement all values or not.