1.3. PullPoint Client Scenario
Overview
In the pull-point client scenario, the pull-point client does not receive messages directly from the broker. Instead, the pull-point client allows messages to accumulate in a remote
PullPoint object (which acts as a message drop-box) and retrieves the messages from time to time by invoking the getMessages operation on the PullPoint. Figure 1.2, “A PullPoint Client Scenario” provides an overview of this scenario.
Figure 1.2. A PullPoint Client Scenario
Clients in this scenario
There are two clients involved in this scenario:
- Publisher client—generates notification messages and publishes the messages on a specific topic, by sending them to the notification broker.
- PullPoint client—a client that uses a polling strategy to get notification messages. Instead of receiving notification messages directly from the broker, this client creates a remote
PullPointinstance. Messages that accumulate in thePullPointcan be retrieved at any time by invoking thegetMessagesoperation on thePullPoint.
Scenario steps
In this scenario, a pull-point client polls for notification messages as follows:
- The pull-point client creates a remote
PullPointinstance by invoking thecreateoperation on theCreatePullPointinterface in the broker. The return value from this operation contains a WS-Addressing reference to the remote pull-point. - The pull-point client creates a subscription by invoking the
subscribeoperation on the broker, passing the following operation arguments:- Topic name—specifies the topic that the client wants to subscribe to.
- Callback reference—a reference to the remote
PullPointinstance that will receive the notifications on behalf of the client.
- A publisher client sends a notification message on a specific topic, by invoking the
notifyoperation on the broker. - At any time, the pull-point client can retrieve messages that have accumulated in the
PullPointinstance by invoking thegetMessagesoperation on thePullPoint.
