Package net.sf.eBus.feed.historic

This package contains a specialized feed providing notification feeds which support both historic and live messages. This capability is provided by two feeds: historic publish feed and historic subscribe feed.

Historic Publish Feed

Like IEPublishFeed, this feed posts live notification messages to eBus if there are any live subscribers listening. The value-added difference is that the historic publish feed persists notifications using the configured IEMessageStore instance. Likewise, the historic publish feed also opens and advertises a request feed for historic request messages. When an historic request is received, the historic notification feed uses IEMessageStore.retrieve(EInterval) method to extract the historic notification messages which are sent back via historic reply messages.

Objects needing to use an historic notification feed must implement IEHistoricPublisher interface. Unlike an EPublisher which should not post notification messages when there are no active subscribers, an historic publisher is clear to post notifications on an open, advertised, and up publish status historic feed because of the need to persist messages.

Historic Subscribe Feed

This feed retrieve both historic and live notification messages and present them as a single continuous stream back to the IEHistoricSubscriber. These notification messages are ordered by timestamp (millisecond granularity), publisher identifier, and message position. For this reason it is important that historic publishers be assigned a unique identifier and that messages be assigned a unique position (especially if messages are posted at a sub-millisecond rate).

Unless the historic subscribe feed is configured to accept notification messages indefinitely, the historic subscriber is informed that the underlying feed has terminated when IEHistoricSubscriber.feedDone() method is called. Once called, this means that the historic subscriber will no longer receive updates.

Another difference between historic and live feeds is that historic subscriber is informed of individual publisher feed status via its feedStatus method. This allows the historic subscriber to determine if there was or is a break in an individual publisher's stream. The feedStatus() method is called for both past and live publisher status updates.

Interface Summary

Interface	Description
HistoricFeedDoneCallback	An eBus client implementing IEHistoricSubscriber may choose to implement this functional interface as a private method instead of implementing the public IEHistoricSubscriber.feedDone(EHistoricSubscribeFeed.HistoricFeedState, EHistoricSubscribeFeed) method.
HistoricFeedStatusCallback	An eBus client implementing IEHistoricSubscriber may choose to implement this functional interface as a private method instead of implementing the public IEHistoricSubscriber.feedStatus(PublishStatusEvent, EHistoricSubscribeFeed) method.
HistoricNotifyCallback	An eBus client implementing IEHistoricSubscriber may choose to implement this functional interface as a private method instead of implementing the public IEHistoricSubscriber.notify(ENotificationMessage, EHistoricSubscribeFeed) method.
HistoricPublishStatusCallback	An eBus client implementing IEHistoricPublisher may choose to implement this functional interface as a private method instead of implementing the public IEHistoricPublisher.publishStatus(EFeedState, EHistoricPublishFeed) method.
IEHistoricPublisher	Classes wanting to send eBus notifications using an EHistoricPublishFeed need to implement this interface.
IEHistoricSubscriber	Classes wanting to receive historic notifications from an historic subscribe feed need to implement this interface.
IEMessageStore	This interface provides EHistoricPublishFeed the ability to persist notification messages and to retrieve those message for a given historic time interval.

Class Summary

Class	Description
EAbstractHistoricFeed<T extends EObject>	Base class for EHistoricPublishFeed and EHistoricSubscribeFeed containing the data members common to each.
EAbstractHistoricFeed.Builder<T extends EObject,F extends EAbstractHistoricFeed<T>,B extends EAbstractHistoricFeed.Builder<T,F,?>>	Base class for EHistoricPublishFeed.Builder and EHistoricSubscribeFeed.Builder subclasses.
EHistoricPublishFeed	The historic publisher feed extends EPublishFeed's ability to publish notification messages to subscribers with the ability to: persist notification messages to a IEMessageStore implementation and handle historic notification requests retrieving previously published messages from message store.
EHistoricPublishFeed.Builder	Builder is used to instantiate EHistoricPublishFeed instances.
EHistoricSubscribeFeed	The historic subscriber feed extends IESubscribeFeed's ability to receive live notification messages with the ability to seamlessly retrieve past notification messages from historic publishers.
EHistoricSubscribeFeed.Builder	Builder is used to instantiate EHistoricSubscribeFeed instances.
EHistoricSubscribeFeed.PastComparator	Comparator used to sort historic notification messages by timestamp, publisher identifier, and message position.
HistoricReply	This reply message contains one or more historic notification message in response to an historic notification request.
HistoricReply.Builder	Builder class for HistoricReply message instances.
HistoricRequest	Request for historic notification messages based on the given date/time interval.
HistoricRequest.Builder	Builder class for HistoricRequest message instances.
PublishStatusEvent	Notification event used to report and persist publish feed status updates.
PublishStatusEvent.Builder	Builder class for PublishStatusEvent message instances.

Enum Summary

Enum	Description
EHistoricSubscribeFeed.HistoricFeedState	Enumerates historic subscribe feed states.
EHistoricSubscribeFeed.TimeLocation	Denotes if a timestamp denotes the past, current time, future, or future on-going.