com.lightstreamer.interfaces.data
Interface ItemEventListener

public interface ItemEventListener

Used by Lightstreamer Kernel to receive the ItemEvents and any asynchronous severe error notification from the Data Adapter. The listener instance is supplied to the Data Adapter by Lightstreamer Kernel through a setListener call. The listener can manage multiple kinds of ItemEvents: ItemEvent objects, OldItemEvent objects, IndexedItemEvent objects and java.util.Map objects. The common characteristics of all these kinds of ItemEvent objects are that:

• they contain the new values and, in some cases, the current values of the Fields of an Item; the Item name is not directly asked to the object.
• they provide an iterator that supplies the names of all the Fields reported in the ItemEvent; the iterator may not be provided if the related Item has been subscribed by setting the needsIterator flag as false.
• they provide a method for getting the value of a Field by name; the value can be expressed either as a String or as a byte array (the special mandatory fields for COMMAND Mode named "key" and "command" must be encoded as String).

When an ItemEvent, of whichever kind, has been sent to the listener, the object instance is totally owned by Lightstreamer Kernel, which may hold it for some time after the listener call has returned. For this reason, the event object should not be used anymore by the Data Adapter and the same holds for any underlying object referenced to by it. Only provided that the event object is thread safe, the object can still be accessed in a read-only way. In particular, if the same event content were to be passed multiple times to the listener (for the same or different items), then passing the same event object instance repeatedly would be allowed. However, specific update methods may pose further restrictions.
If ItemEvents are implemented as wrappers of the data objects received from the external feed (like JMS Messages), the above has to be carefully considered.

See Also:

DataProvider

Method Summary

void	endOfSnapshot(java.lang.String itemName) Called by a Data Adapter to signal to Lightstreamer Kernel that no more ItemEvent belonging to the Snapshot are expected for an Item.
void	failure(java.lang.Throwable e) Called by a Data Adapter to notify Lightstreamer Kernel of the occurrence of a severe problem that can compromise future operation of the Data Adapter.
void	smartEndOfSnapshot(java.lang.Object itemHandle) Can be called, instead of endOfSnapshot, by a Data Adapter that implements the extended interface SmartDataProvider, in all cases in which endOfSnapshot can be called.
void	smartUpdate(java.lang.Object itemHandle, IndexedItemEvent event, boolean isSnapshot) Can be called by a Data Adapter that implements the extended interface SmartDataProvider to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an IndexedItemEvent instance.
void	smartUpdate(java.lang.Object itemHandle, ItemEvent event, boolean isSnapshot) Can be called by a Data Adapter that implements the extended interface SmartDataProvider to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an ItemEvent instance.
void	smartUpdate(java.lang.Object itemHandle, java.util.Map event, boolean isSnapshot) Can be called by a Data Adapter that implements the extended interface SmartDataProvider to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as a java.util.Map instance.
void	smartUpdate(java.lang.Object itemHandle, OldItemEvent event, boolean isSnapshot) Can be called by a Data Adapter that implements the extended interface SmartDataProvider to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an OldItemEvent instance.
void	update(java.lang.String itemName, IndexedItemEvent event, boolean isSnapshot) Called by a Data Adapter to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an IndexedItemEvent instance.
void	update(java.lang.String itemName, ItemEvent event, boolean isSnapshot) Called by a Data Adapter to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an ItemEvent instance.
void	update(java.lang.String itemName, java.util.Map event, boolean isSnapshot) Called by a Data Adapter to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as a java.util.Map instance.
void	update(java.lang.String itemName, OldItemEvent event, boolean isSnapshot) Called by a Data Adapter to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an OldItemEvent instance.

Method Detail

update

void update(java.lang.String itemName,
            ItemEvent event,
            boolean isSnapshot)

Called by a Data Adapter to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an ItemEvent instance.
The Adapter should ensure that, after an unsubscribe call for the item has returned, no more update calls are issued, until requested by a new subscription for the same item. This assures that, upon a new subscription for the item, no trailing events due to the previous subscription can be received by the Kernel. Note that the method is nonblocking; moreover, it only takes locks to first order mutexes; so, it can safely be called while holding a custom lock.

Parameters:

itemName - The name of the Item whose values are carried by the ItemEvent.

event - An ItemEvent instance.

isSnapshot - true if the ItemEvent carries the Item Snapshot.

See Also:

DataProvider

update

void update(java.lang.String itemName,
            OldItemEvent event,
            boolean isSnapshot)

Called by a Data Adapter to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an OldItemEvent instance.
The Adapter should ensure that, after an unsubscribe call for the item has returned, no more update calls are issued, until requested by a new subscription for the same item. This assures that, upon a new subscription for the item, no trailing events due to the previous subscription can be received by the Kernel. Note that the method is nonblocking; moreover, it only takes locks to first order mutexes; so, it can safely be called while holding a custom lock.

Parameters:

itemName - The name of the Item whose values are carried by the ItemEvent.

event - An OldItemEvent instance.

isSnapshot - true if the ItemEvent carries the Item Snapshot.

See Also:

DataProvider

update

void update(java.lang.String itemName,
            java.util.Map event,
            boolean isSnapshot)

Called by a Data Adapter to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as a java.util.Map instance.
The Adapter should ensure that, after an unsubscribe call for the item has returned, no more update calls are issued, until requested by a new subscription for the same item. This assures that, upon a new subscription for the item, no trailing events due to the previous subscription can be received by the Kernel. Note that the method is nonblocking; moreover, it only takes locks to first order mutexes; so, it can safely be called while holding a custom lock.
If the event object is of type java.util.HashMap, then Lightstreamer Kernel, in order to improve performances, may synchronize on the object lock and modify the object contents while processing it. As a consequence, in this case, the event object, once passed to the listener, cannot be accessed anymore by the Data Adapter, even for reading (it can still be passed multiple times to the listener, if needed).

Parameters:

itemName - The name of the Item whose values are carried by the ItemEvent.

event - A java.util.Map instance, in which Field names are associated to Field values. A value can be expressed as either a String or a byte array, the latter case being the most efficient, though restricted to the ISO-8859-1 (ISO-LATIN-1) character set. A Field value can be null or missing if the Field is not to be reported in the event.

isSnapshot - true if the ItemEvent carries the Item Snapshot.

See Also:

DataProvider

update

void update(java.lang.String itemName,
            IndexedItemEvent event,
            boolean isSnapshot)

Called by a Data Adapter to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an IndexedItemEvent instance.
The Adapter should ensure that, after an unsubscribe call for the item has returned, no more update calls are issued, until requested by a new subscription for the same item. This assures that, upon a new subscription for the item, no trailing events due to the previous subscription can be received by the Kernel. Note that the method is nonblocking; moreover, it only takes locks to first order mutexes; so, it can safely be called while holding a custom lock.

Parameters:

itemName - The name of the Item whose values are carried by the ItemEvent.

event - An IndexedItemEvent instance.

isSnapshot - true if the ItemEvent carries the Item Snapshot.

See Also:

DataProvider

smartUpdate

void smartUpdate(java.lang.Object itemHandle,
                 ItemEvent event,
                 boolean isSnapshot)

Can be called by a Data Adapter that implements the extended interface SmartDataProvider to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an ItemEvent instance.
This method should not be called while holding custom locks. After that an unsubscribe call for the item has returned, further calls of this method for the itemHandler received with the last subscription operation are still allowed and will be just discarded.

Parameters:

itemHandle - Identifies the Item whose values are carried by the ItemEvent. It must be the same object received in the subscribe call.

event - An ItemEvent instance.

isSnapshot - true if the ItemEvent carries the Item Snapshot.

See Also:

SmartDataProvider

smartUpdate

void smartUpdate(java.lang.Object itemHandle,
                 OldItemEvent event,
                 boolean isSnapshot)

Can be called by a Data Adapter that implements the extended interface SmartDataProvider to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an OldItemEvent instance.
This method should not be called while holding custom locks. After that an unsubscribe call for the item has returned, further calls of this method for the itemHandler received with the last subscription operation are still allowed and will be just discarded.

Parameters:

itemHandle - Identifies the Item whose values are carried by the ItemEvent. It must be the same object received in the subscribe call.

event - An OldItemEvent instance.

isSnapshot - true if the ItemEvent carries the Item Snapshot.

See Also:

SmartDataProvider

smartUpdate

void smartUpdate(java.lang.Object itemHandle,
                 java.util.Map event,
                 boolean isSnapshot)

Can be called by a Data Adapter that implements the extended interface SmartDataProvider to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as a java.util.Map instance.
This method should not be called while holding custom locks. After that an unsubscribe call for the item has returned, further calls of this method for the itemHandler received with the last subscription operation are still allowed and will be just discarded.
If the event object is of type java.util.HashMap, then Lightstreamer Kernel, in order to improve performances, may synchronize on the object lock and modify the object contents while processing it. As a consequence, in this case, the event object, once passed to the listener, cannot be accessed anymore by the Data Adapter, even for reading (it can still be passed multiple times to the listener, if needed).

Parameters:

itemHandle - Identifies the Item whose values are carried by the ItemEvent. It must be the same object received in the subscribe call.

event - A java.util.Map instance, in which Field names are associated to Field values.

isSnapshot - true if the ItemEvent carries the Item Snapshot.

See Also:

SmartDataProvider

smartUpdate

void smartUpdate(java.lang.Object itemHandle,
                 IndexedItemEvent event,
                 boolean isSnapshot)

Can be called by a Data Adapter that implements the extended interface SmartDataProvider to send an ItemEvent to Lightstreamer Kernel when the ItemEvent is implemented as an IndexedItemEvent instance.
This method should not be called while holding custom locks. After that an unsubscribe call for the item has returned, further calls of this method for the itemHandler received with the last subscription operation are still allowed and will be just discarded.

Parameters:

itemHandle - Identifies the Item whose values are carried by the ItemEvent. It must be the same object received in the subscribe call.

event - An IndexedItemEvent instance.

isSnapshot - true if the ItemEvent carries the Item Snapshot.

See Also:

SmartDataProvider

endOfSnapshot

void endOfSnapshot(java.lang.String itemName)

Called by a Data Adapter to signal to Lightstreamer Kernel that no more ItemEvent belonging to the Snapshot are expected for an Item. This call is optional, because the Snapshot completion can also be inferred from the isSnapshot flag in the update and smartUpdate calls. However, this call allows Lightstreamer Kernel to be informed of the Snapshot completion before the arrival of the first non-snapshot event. Calling this function is recommended if the Item is to be subscribed in DISTINCT mode. In case the Data Adapter returned false to isSnapshotAvailable for the same Item, this function should not be called.
The Adapter should ensure that, after an unsubscribe call for the item has returned, possible pending endOfSnapshot calls related with the previous subscription request are no longer issued. This assures that, upon a new subscription for the item, no trailing events due to the previous subscription can be received by the Kernel. Note that the method is nonblocking; moreover, it only takes locks to first order mutexes; so, it can safely be called while holding a custom lock.

Parameters:

itemName - The name of the Item whose snapshot has been completed.

See Also:

DataProvider

smartEndOfSnapshot

void smartEndOfSnapshot(java.lang.Object itemHandle)

Can be called, instead of endOfSnapshot, by a Data Adapter that implements the extended interface SmartDataProvider, in all cases in which endOfSnapshot can be called.
This method should not be called while holding custom locks. After that an unsubscribe call for the item has returned, further calls of this method for the itemHandler received with the last subscription operation are still allowed and will be just discarded.

Parameters:

itemHandle - Identifies an Item whose snapshot has been completed.

See Also:

endOfSnapshot(java.lang.String), SmartDataProvider

failure

void failure(java.lang.Throwable e)

Called by a Data Adapter to notify Lightstreamer Kernel of the occurrence of a severe problem that can compromise future operation of the Data Adapter. This causes the whole Server to exit, so that an external recovery mechanism may come into action.

Parameters:

e - any java.lang.Throwable object, with the description of the problem.