com.dxfeed.api.osub

Interface ObservableSubscriptionChangeListener

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface ObservableSubscriptionChangeListener

The listener interface for receiving notifications on the changes of observed subscription. All methods on this interface are invoked while holding a lock on ObservableSubscription instance, thus all changes for a given subscription are synchronized with respect to each other.

Decorated symbols

The sets of symbols that are passed to symbolsAdded(Set) and symbolsRemoved(Set) are decorated depending on the actual implementation class of DXFeedSubscription. DXFeedTimeSeriesSubscription decorates original subscription symbols by wrapping them into instances of TimeSeriesSubscriptionSymbol class.

Equality of symbols and notifications

Symbols are compared using their equals method. When one symbol in subscription is replaced by the other one that is equal to it, then the decision of whether to issue symbolsAdded notification is up to implementation.

In particular, DXFeedSubscription uses its implementation of shallNotifyOnSymbolUpdate method to figure out what to do in this case. Its default implementation is designed so that repeated additions of the same String symbol do not result in notification, while repeated additions of FilteredSubscriptionSymbol instances like TimeSeriesSubscriptionSymbol objects get notification.

However, the implementation that is returned by DXPublisher.getSubscription can generate repeated symbolsAdded notifications to its listeners for the same symbols without the corresponding symbolsRemoved notifications in between them. It happens when subscription disappears, cached data is lost, and subscription reappears again. On each symbolsAdded notification data provider shall publish the most recent events for the corresponding symbols.

Wildcard symbols

The set of symbols may contain WildcardSymbol.ALL object. See WildcardSymbol for details.

Method Summary

Modifier and Type	Method and Description
default void	subscriptionClosed() Invoked after subscription is closed or when this listener is removed from the subscription.
void	symbolsAdded(Set<?> symbols) Invoked after a collection of symbols is added to a subscription.
default void	symbolsRemoved(Set<?> symbols) Invoked after a collection of symbols is removed from a subscription.

Method Detail

symbolsAdded

void symbolsAdded(Set<?> symbols)

Invoked after a collection of symbols is added to a subscription. Subscription's set of symbols already includes added symbols when this method is invoked. The set of symbols is decorated.

symbolsRemoved

default void symbolsRemoved(Set<?> symbols)

Invoked after a collection of symbols is removed from a subscription. Subscription's set of symbols already excludes removed symbols when this method is invoked. The set of symbols is decorated. Default implementation is empty.

subscriptionClosed

default void subscriptionClosed()

Invoked after subscription is closed or when this listener is removed from the subscription. DXPublisher subscription is considered to be closed when the corresponding DXEndpoint is closed. Default implementation is empty.