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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 PullPoint instance. Messages that accumulate in the PullPoint can be retrieved at any time by invoking the getMessages operation on the PullPoint.

Scenario steps

In this scenario, a pull-point client polls for notification messages as follows:
  1. The pull-point client creates a remote PullPoint instance by invoking the create operation on the CreatePullPoint interface in the broker. The return value from this operation contains a WS-Addressing reference to the remote pull-point.
  2. The pull-point client creates a subscription by invoking the subscribe operation 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 PullPoint instance that will receive the notifications on behalf of the client.
  3. A publisher client sends a notification message on a specific topic, by invoking the notify operation on the broker.
  4. At any time, the pull-point client can retrieve messages that have accumulated in the PullPoint instance by invoking the getMessages operation on the PullPoint.
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