org.olap4j
Interface CellSetListener


public interface CellSetListener

Listener interface for receiving events when the contents of a CellSet have changed.

NOTE: This functionality is experimental and is subject to change or removal without notice.

The client can ask the server to provide the listener with a specific granularity of events, but the server can decline to provide that granularity.

Fine granularity deals with changes such as cell values changing (and reports the before and after value, before and after formatted value), positions being deleted, positions being changed.

When an atomic change happens on the server (say a cache flush, if the server is mondrian) then an event will arrive on the client containing all of those changes. Although CellSetListener.CellSetChange.getCellChanges() and CellSetListener.CellSetChange.getAxisChanges() return lists, the client should assume that all of the events in these lists simultaneously.

At any point, the server is free to throw up its hands and say 'there are too many changes' by sending null values for getCellChanges or getAxisChanges. This prevents situations where there are huge numbers of changes that might overwhelm the server, the network link, or the client, such as might happen if a large axis is re-sorted.

The client should always be ready for that to happen (even for providers that claim to provide fine granularity events), and should re-execute the query to get the cell set. In fact, we recommend that clients re-execute the query to get a new cellset whenever they get an event. Then the client can use the details in the event to highlight cells that have changed.

Notes for implementors

The purpose of registering a listener before creating a cell set is to ensure that no events "leak out" between creating a cell set and registering a listener, or while a statement is being re-executed to produce a new cell set.

The cellSetOpened(CellSet) and cellSetClosed(CellSet) methods are provided so that the listener knows what is going on when a statement is re-executed. In particular, suppose a statement receives an change event decides to re-execute. The listener is attached to the statement, so receives notifications about both old and new cell sets. The driver implicitls closes the previous cell set and calls cellSetClosed, then calls cellSetOpened with the new cell set.

If changes are occurring regularly on the server, there will soon be a call to cellSetChanged(org.olap4j.CellSetListener.CellSetChange). It is important to note that this event contains only changes that have occurred since the new cell set was opened.

The granularity parameter is provided to OlapStatement.addListener(org.olap4j.CellSetListener.Granularity, org.olap4j.CellSetListener) for the server's benefit. If granularity is only CellSetListener.Granularity.COARSE, the server may be able to store less information in order to track the cell set.

Version:
$Id: CellSetListener.java 482 2012-01-05 23:27:27Z jhyde $

Nested Class Summary
static interface CellSetListener.AxisChange
          Description of a change to a particular CellSetAxis; part of a CellSetListener.CellSetChange.
static interface CellSetListener.CellChange
          Description of a change to a particular Cell; part of a CellSetListener.CellSetChange.
static interface CellSetListener.CellSetChange
          Description of changes that have occurred to the cell set.
static class CellSetListener.Granularity
          Granularity of notifications that should be sent to a cellset listener.
 
Method Summary
 void cellSetChanged(CellSetListener.CellSetChange cellSetChange)
          Invoked when a cell set has changed.
 void cellSetClosed(CellSet cellSet)
          Invoked when a cell set is closed.
 void cellSetOpened(CellSet cellSet)
          Invoked when a cell set is opened.
 

Method Detail

cellSetOpened

void cellSetOpened(CellSet cellSet)
Invoked when a cell set is opened.

Parameters:
cellSet - Cell set

cellSetClosed

void cellSetClosed(CellSet cellSet)
Invoked when a cell set is closed.

Parameters:
cellSet - Cell set

cellSetChanged

void cellSetChanged(CellSetListener.CellSetChange cellSetChange)
Invoked when a cell set has changed.

Parameters:
cellSetChange - Change descriptor

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