Implementation note: While the specification allows a driver to block on I/O in a MongoClient or MongoClientURI constructor, that's likely not a good option for the Java driver. Blocking in constructors or factory methods is unfriendly to IOC containers like Spring and should be avoided. However, it's not clear exactly how the Java driver should do this. The problem is that MongoClientURI has a method #getClientOptions which is supposed to provide the final immutable options for a MongoClient. But the spec requires that options are also read from a DNS TXT record, which is blocking.