Channel Joins

Channel joins can be created using the nmakechanjoin join sample application which is provided in the bin directory of the Universal Messaging installation. For further information on using this example please see the Make Channel Join example page.

Universal Messaging joins are created as follows:

//Obtain a reference to the source channel
nChannel mySrcChannel = mySession.findChannel( nca );

//Obtain a reference to the destination channel
nChannel myDstChannel = mySession.findChannel( dest );

//create the join
mySrcChannel.joinChannel( myDstChannel, true, jhc, SELECTOR );

Channel joins can also be deleted. Please see the Delete Channel Join example for more information.

It is possible to archive messages from a given channel by using an archive join. To perform an archive join, the destination must be a queue in which the archived messages will be stored. An example of this can be seen below:

Since this is an archive join, all events matching the optional selector parameter(all events if no selector is specified) will be put into the archive queue, by design this includes all duplicate events published to the source.

nChannelAttributes archiveAtr = new nChannelAttributes();
archiveAtr.setName(rchanName);
nQueue archiveQueue = mySession.findQueue(archiveAtr);
mySrcChannel.joinChannelToArchive(archiveQueue);

Inter-cluster joins are added and deleted in almost exactly the same way as normal joins. The only differences are that the two clusters must have an inter-cluster connection in place, and that since the clusters do not share a namespace, ech channel must be retrieved from nodes in their respective clusters, rather than through the same node. For example :

nChannel cluster1chan1 = realmNode1.findChannel(channelattributes1);
nChannel cluster2chan1 = realmNode4.findChannel(channelattributes2);
cluster1chan1.joinChannel(cluster2chan1);

Inter-Cluster joins can also be created through the Enterprise Manager.

Universal Messaging offers the ability to forward data received on one independent realm or cluster to many other independent realms or clusters, which may reside in geographically distinct locations. Traditionally this is done using the Join mechanism, which will forward all events from one channel to another.

There is an alternative mechanism, namely Interest Propagation. This mechanism expands upon the functionality provided by joins by providing the ability to forward events only when there are subscribers to a channel of the same name on the remote realm or cluster. Forwarding only events which have an active subscription reduces the number of events and bandwidth used on these links.

Realms and clusters keep track of interest on remote realms that they have a direct connection to. This means that beyond the initial setup of a channel, no further configuration is required.

Managing interest on a remote realm is done programmatically using the Universal Messaging Administrative API. Each channel present on a realm or cluster can be linked to a pair of attributes canSend and canReceive.

Enabling the canReceive attribute on a channel of a realm or cluster will enable this realm or cluster to receive information on the given channel from other directly connected realms or clusters that have a channel of the same name. The realm or cluster notifies all connected realms when this attribute changes for a given channel.

Data is only forwarded from a realm or cluster to a remote realm or cluster if all of the following conditions are met:

Enabling the canSend attribute on a channel in a realm or cluster will enable this realm or cluster to begin forwarding data to other realms or clusters it is aware of. Data is forwarded to every realm which the source realm is aware of that has a channel with the same name and is able to receive the event (it has the canReceive flag enabled and has an interested subscriber).

All installations of Universal Messaging come with a sample application called interestmanagerutility. This is an application which takes a series of commands to manage the interest properties for a given set of realms.