WebSphere Business Integration Adapters: An Adapter Development and WebSphere Business Integration Solution

90 WebSphere Business Integration Adapters

8.1 Overview of event notification

The ways in which application-specific components detect and retrieve events

differ from one adapter to another. However, the way in which

application-specific components send events to the Adapter Framework and the

way in which the Adapter Framework delivers those events to the integration

broker is standard across all adapters.

When an event occurs in an application, the connector application-specific

component processes the event, retrieves related application data, and returns

the data to the integration broker in a business object. The following steps outline

the tasks of an event-notification mechanism:

1. An application performs an event and puts an event record into the event

store. The

event store is a persistent cache in the application where event

records are saved until the connector can process them. The event record

contains information about the change to an event store in the application.

This information includes the data that has been created or changed, as well

as the operation (such as create, delete, or update) that has been performed

on the data.

2. The connector’s application-specific component monitors the event store,

usually through a polling mechanism, to check for incoming events. When it

finds an event, it retrieves its event record from the event store and converts it

into an application-specific business object with a verb.

3. Before sending the business object to the integration broker, the

application-specific component can verify that the integration broker is

interested in receiving the business object.

If you use WebSphere InterChange Server as the business integration

system, the Adapter Framework does not assume that the integration broker

is always interested in every supported business object. At initialization, the

Adapter Framework requests its subscription list from the Connector

Controller. At run-time, the application-specific component can query the

Adapter Framework to verify that some collaboration subscribes to a

particular business object. The application-specific connector component can

send the event only if some collaboration is currently subscribed. The

application-specific component sends the event, in the form of a business

object and a verb, to the Adapter Framework, which in turn sends it to the

Connector Controller within InterChange Server.

However, if you use the Message Broker or WebSphere Application Server

(Server Foundation) as the business integration system, the Adapter

Framework assumes that the integration broker is interested in all the

connector’s supported business objects. If the application-specific connector

component queries the Adapter Framework to verify whether to send the

Chapter 8. Asynchronous event processing and notification 91

business object, it will receive a confirmation for every business object that

the connector supports.

4. If the integration broker is interested in the business object, the connector

application-specific component sends the event, in the form of a business

object and a verb, to the Adapter Framework, which in turn sends it to the

integration broker.

The implementation of an event-notification mechanism is a three-stage process:

1. Create an event store that the application uses to hold notifications of events

that have changed application business entities.

2. Implement an event detection mechanism within the application. Event

detection notices a change in an application entity and writes an event record

containing information about the change to an event store in the application.

3. Implement an event retrieval mechanism (such as a polling mechanism)

within the connector to retrieve events from the event store and take the

appropriate action to notify other applications.

Figure 8-1 illustrates the components of the event-notification mechanism. In

event notification, the flow of information is from the application to the connector

and then to the integration broker.

Figure 8-1 Event detection and retrieval mechanism

In many cases, an application must be configured or modified before the

connector can use the event-notification mechanism. Typically, this application

configuration occurs as part of the installation of the connector’s

application-specific component. Modifications to the application might include

setting up a user account in the application, creating an event store and event

Event

Record

Event

Event

Retrieval

User

Action

Application

Entity

Application

Connector

Framework

Event

Store

Integration

Broker

Event

Detection

Information Flow