Uniqueness of Subscriptions
Each subscription that your BrokerClient registers is considered to be unique, based on the event type name and filter specified. After you have registered a subscription for a particular event type name and filter combination, any attempts to register another subscription with the same combination will be ignored.
Note:
The BrokerClient.newSubscription method will not throw an exception if you attempt to register the same subscription more than once, it will simply ignore the request.
You can use the BrokerClient.doesSubscriptionExist method to determine whether a subscription has already been registered.