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

Chapter 8. Asynchronous event processing and notification 115

The SQL statement Example 8-1 shows how a connector might select event

records based on event priority. The SELECT statement sorts the events by

priority, and the connector processes each event in turn.

Example 8-1 Example SQL statement

SELECT event_id, object_name, object_verb, object_key

FROM event_table

WHERE event_status = 0 ORDER BY event_priority

8.3.6 Event distribution

The polling mechanisms can be implemented so that multiple connectors can

poll the same event store. Each connector can be configured to process certain

events, create specific business objects, and pass those business objects to

broker system. This configuration can streamline the processing of certain types

of events and increase the transfer of data out of an application.

To implement event distribution so that multiple connectors can poll the event

store, complete the following steps:

1. Add a column to the event record for an integer connector identifier (ID), and

design the event detection mechanism to specify which connector will pick up

the event. This might be done per application entity. For example, the event

detection mechanism might specify that all Customer events be picked up by

the connector that has the connectorId field set to 4.

2. Add an application-specific connector property named ConnectorId. Assign

each connector a unique identifier and store this value in its ConnectorId

property.

Implement the poll method to query for the value of the ConnectorId property. If

the property is not set, the poll method can retrieve all event records from the

event store as usual. If the property is set to a connector identifier value, the poll

method retrieves only those events that match the ConnectorId property.

8.4 Custom pollForEvents() method

For a Java connector, the CWConnectorAgent class defines the

pollForEvents() method. This class provides a default implementation of the

pollForEvents() method. You can use this default implementation or override

the method with your own poll method. However, the pollForEvents() method

must be implemented.

116 WebSphere Business Integration Adapters

The Java-based pseudo-code in Example 8-2 shows the basic logic flow for a

pollForEvents() method (see 8.3.2, “Basic logic for the poll method” on

page 112 for more details).

Example 8-2 Basic logic of the pollForEvents() method

public int pollForEvents() {

int status = 0;

get the events from the event store

for (events 1 to MaxEvents in event store) {

extract BOName, verb, and key from the event record

if(ConnectorBase.isSubscribed(BOName,BOverb) {

BO = JavaConnectorUtil.createBusinessObject(BOName)

BO.setAttrValue(key)

retrieve application data using doVerbFor()

BO.setVerb(Retrieve)

BO.doVerbFor()

BO.setVerb(BOverb)

status = gotApplEvent(BusinessObject);

archive event record with success or failure status

} else {

archive item with unsubscribed status

}

return status;

}

The method first retrieves a set of events from the event store. For each event,

the method calls the isSubscribed() method to determine whether any

subscriptions exist for the corresponding business object. If there are

subscriptions, the method retrieves the data from the application, creates a new

business object, and calls the gotApplEvent() method to send the business

object to InterChange Server. If there are no subscriptions, the method archives

the event record with a status value of unprocessed.

The steps in the basic logic for the event processing that the pollForEvents()

method typically performs are:

1. Set up a subscription manager for the connector.

2. Verify that the connector still has a valid connection to the event store.

Note: For a flow chart of the poll method’s basic logic, see Figure 8-6 on

page 111.