1.2. Consumer Client Scenario

Overview

In the consumer client scenario, the consumer client receives messages directly from the broker, as soon as they become available. This approach requires the consumer client to implement a callback object, which exposes a Web service endpoint. Figure 1.1, “A Consumer Client Scenario” provides an overview of this scenario.

Figure 1.1. A Consumer 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.
  • Consumer client—a client that implements a consumer callback object (exposing a Web service endpoint of NotificationConsumer type), which is capable of receiving notifications directly from the notification broker.

Scenario steps

In this scenario, a consumer client receives notification messages from the broker as follows:
  1. The consumer client instantiates a consumer callback object, which implements the NotificationConsumer interface and is capable of receiving notifications from the broker.
  2. The consumer 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 consumer callback object that will receive the notifications, where the service reference has the format of a WS-Addressing Endpoint Reference (EPR).
  3. A publisher client sends a notification message on a specific topic, by invoking the notify operation on the broker.
  4. If the message topic matches the consumer client's subscription, the broker will forward the message to the consumer client by invoking the notify operation on the consumer callback service.