I had redeployed spring web application onto glassfish 3.1, I got endless NullPointerException at at com.mongodb.OutMessage.reset(OutMessage.java:73).
(you can also refer this page - http://groups.google.com/group/mongodb-user/browse_thread/thread/a51a1f5f3850ba46/74272391a3ee37ab?hl=en&lnk=gst&q=endless#74272391a3ee37ab )

Here is server log:
[#|2011-05-12T01:05:37.251+0900|SEVERE|glassfish3.1|com.mongodb.ReplicaSetS tatus|_ThreadID=27;_ThreadName=Thread-1;|unexpected
error getting config from node: localhost:10001
java.lang.NullPointerException
at com.mongodb.OutMessage.reset(OutMessage.java:73)
at com.mongodb.OutMessage.<init>(OutMessage.java:51)
at com.mongodb.OutMessage.query(OutMessage.java:38)
at com.mongodb.DBPort.findOne(DBPort.java:142)
at com.mongodb.ReplicaSetStatus$Node.update(ReplicaSetStatus.java:156)
at com.mongodb.ReplicaSetStatus.updateAll(ReplicaSetStatus.java:277)
at com.mongodb.ReplicaSetStatus$Updater.run(ReplicaSetStatus.java:238)

How to reproduce this issue:
1. deploy application to glassfish
2. redeploy same application to glassfish (or, drop the application from the glassfish)
3. you can get that exception endless

I inject MongoDB Connecter as spring bean.
<bean id="MongoConnector" class="jwdm.core.bean.MongoConnector"
p:host="localhost" p:port="10001">

Here is full code of MongoConnector (as Spring bean):
public class MongoConnector {
private Mongo mongoDB;
private String host;
private String port;
// Return an instance of Mongo
public Mongo getMongo() {
logger.debug("Retrieving MongoDB");
if (mongoDB == null) {
try

{ List<ServerAddress> addrs = new ArrayList<ServerAddress>(); addrs.add(new ServerAddress(host, Integer.parseInt(port))); mongoDB = new Mongo(addrs); }

catch (UnknownHostException e)

{ logger.error(e.toString()); } catch (MongoException e) { logger.error(e.toString()); }

}
return mongoDB;
}
// Retrieve a db
public DB getDB(String dbname)

{ logger.debug("Retrieving db: " + dbname); return getMongo().getDB(dbname); }

// Retrieve a collection
public DBCollection getCollection(String dbname, String collection)

{ logger.debug("Retrieving collection: " + collection); return getDB(dbname).getCollection(collection); }

... getter , setter ...
}
</bean>

Before using spring bean style, I was using static factory style without spring.
But it produces same exception.

Here is static factory style code:

public class MongoDBFactory {

protected static Logger logger = LoggerFactory.getLogger(MongoDBFactory.class);

private static Mongo mongoDB;

// Make sure no one can instantiate our factory
private MongoDBFactory() {
}

// Return an instance of Mongo
public static Mongo getMongo() {
logger.debug("Retrieving MongoDB");
if (mongoDB == null) {
try

{ List<ServerAddress> addrs = new ArrayList<ServerAddress>(); addrs.add(new ServerAddress("localhost", 10001)); //addrs.add(new ServerAddress("leewin12.cafe24.com", 10001)); mongoDB = new Mongo(addrs); }

catch (UnknownHostException e)

{ logger.error(e.toString()); } catch (MongoException e) { logger.error(e.toString()); }

}

return mongoDB;
}

// Retrieve a db
public static DB getDB(String dbname)

{ logger.debug("Retrieving db: " + dbname); return getMongo().getDB(dbname); }

// Retrieve a collection
public static DBCollection getCollection(String dbname, String collection)

{ logger.debug("Retrieving collection: " + collection); return getDB(dbname).getCollection(collection); }

}

Thank you for your helps,
Greg