MongoDB JavaEE Singleton Extra Instances

Question

So, i've been having this small issue while attempting to use MongoDB (And java driver), using Servlets EJBs and EJB Timers, running on Jboss 4.2.3.

I create a mongo singleton like so

private static Mongo mongoSingleton = null;

private MongoSingleton()
{

}

public synchronized static Mongo getMongo() throws UnknownHostException
{
     if(mongoSingleton == null)
     {
         MongoOptions options = new MongoOptions();
         options.connectionsPerHost = 40;
         mongoSingleton = new Mongo("localhost", options); 
     }
     return mongoSingleton;
}

and then pass the instance between my stateless session beans (Which i use for database transactions) using

DB db = MongoSingleton.getMongo().getDB("data");

Unless i'm missing something, surely this should use the single instance created in the singleton, however when i check the Mongo console, i notice that extra connections are being created in the application after the Mongo instance is created, this seems to happen at odd times (Does not happen at every database transaction), and the mongoSingleton is never null after the initial instance is created.

I may be missing something simple, but any tips would be handy, cheers.

Sorry, forgot to include that part in the Copy/Paste, i've got that in there. — user2351681, May 05 '13 at 10:56
[What is an efficient way to implement a singleton pattern in Java?](http://stackoverflow.com/questions/70689/) — fredoverflow, May 05 '13 at 13:13

score 0 · Answer 1 · answered May 05 '13 at 13:26

0

How about you put some debug output into your constructor?

private MongoSingleton()
{
    long threadId = Thread.currentThread().getId();
    System.out.println("New instance created from thread " + threadId);
}

You can also set a breakpoint at that line to understand when exactly another instance is created.

answered May 05 '13 at 13:26

fredoverflow

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I have done, the only instance is created on startup by threadid 14, after that no instances are created, but connections keep opening, its pretty odd. – user2351681 May 05 '13 at 13:43
You're not by any chance serializing your singleton, right? Apart from that, I'm out of ideas, sorry. – fredoverflow May 05 '13 at 14:02
Nope, i'm not. Thanks anyway though. – user2351681 May 05 '13 at 14:05

MongoDB JavaEE Singleton Extra Instances

1 Answers1