org.apache.sling.discovery.commons.providers

Class BaseTopologyView

java.lang.Object

org.apache.sling.discovery.commons.providers.BaseTopologyView

All Implemented Interfaces:

TopologyView

public abstract class BaseTopologyView
extends java.lang.Object
implements TopologyView

Very simple abstract base class for the TopologyView which comes with the 'setNotCurrent()' method - that allows the ViewStateManager to mark a topologyView as no longer current - and the isCurrent() is handled accordingly.

Constructor Summary

Constructors

Constructor and Description
BaseTopologyView()

Method Summary

Modifier and Type	Method and Description
InstanceDescription	getInstance(java.lang.String slingId) Simple getter for a particular slingId
abstract java.lang.String	getLocalClusterSyncTokenId() Returns the id that shall be used in the syncToken by the ClusterSyncService.
boolean	isCurrent() Checks if this TopologyView is currently valid - or if the service knows of a topology change just going on (or another uncertainty about the topology such as IOException etc)
void	setNotCurrent() Marks this view as no longer current - this typically results in a TOPOLOGY_CHANGING event to be sent.
java.lang.String	toShortString()

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.apache.sling.discovery.TopologyView

findInstances, getClusterViews, getInstances, getLocalInstance

Constructor Detail

BaseTopologyView

public BaseTopologyView()

Method Detail

isCurrent

public boolean isCurrent()

Checks if this TopologyView is currently valid - or if the service knows of a topology change just going on (or another uncertainty about the topology such as IOException etc)

Specified by:

isCurrent in interface TopologyView

Returns:

true if this TopologyView is currently valid, false if the service knows of a topology change just going on (or another issue with discovery like IOException etc)

setNotCurrent

public void setNotCurrent()

Marks this view as no longer current - this typically results in a TOPOLOGY_CHANGING event to be sent.

Note that once marked as not current, it can no longer be reverted to current==true

getLocalClusterSyncTokenId

public abstract java.lang.String getLocalClusterSyncTokenId()

Returns the id that shall be used in the syncToken by the ClusterSyncService.

The clusterSyncId uniquely identifies each change of the local cluster for all participating instances. That means, all participating instances know of the clusterSyncId and it is the same for all instances. Whenever an instance joins/leaves the cluster, this clusterSyncId must change.

Since this method returns the *local* clusterSyncId, it doesn't care if a remote cluster experienced changes - it must only change when the local cluster changes. However, it *can* change when a remote cluster changes too. So the requirement is just that it changes *at least* when the local cluster changes - but implementations can opt to regard this rather as a TopologyView-ID too (ie an ID that identifies a particular incarnation of the TopologyView for all participating instances in the whole topology).

This id can further safely be used by the ClusterSyncService to identify a syncToken that it writes and that all other instances in the lcoal cluster wait for, before sending a TOPOLOGY_CHANGED event.

Note that this is obviously not to be confused with the ClusterView.getId() which is stable throughout the lifetime of a cluster.

toShortString

public java.lang.String toShortString()

getInstance

public InstanceDescription getInstance(java.lang.String slingId)

Simple getter for a particular slingId

Parameters:

slingId - the slingId for which to lookup the InstanceDescription

Returns:

the InstanceDescription matching the provided slingId - or null if it doesn't exist