I have a requirement to publish (to Graphite) the 'number of active connection available' status of a Mongo db instance when a REST service is called. I know we can use db.serverStatus() to know the details of connections on the server side. I am looking to get the 'number of active connections available' information on the client side using JAVA API. The MongoDB Java Driver API documentation doesn't help much on it.
Assuming you are using the 3.0.x driver, and connecting to localhost on default port:
MongoClient mongoClient = new MongoClient();
MongoDatabase database = mongoClient.getDatabase("admin");
Document serverStatus = database.runCommand(new Document("serverStatus", 1));
Map connections = (Map) serverStatus.get("connections");
Integer current = (Integer) connections.get("current");