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

Chapter 17. Implementing event notification 281

17.2 Implementing the fetchEvents() method

The fetchEvents() method retrieves a specified number of ready-for-poll events

from the event store. This method searches the event store for event records

with the READY_FOR_POLL status and puts them in the eventsToProcess

vector.

The number of events that the fetchEvents() method retrieves is determined by

the value of the PollQuantity connector configuration property. For each retrieved

event, the method must create a CWConnectorEvent event object and put this

event object into a Java vector. The method then calls the setEventsToProcess()

method to save this event vector into the eventsToProcess vector, which is a

member of the CWConnectorEventStore object.

The fetchEvents() method determines the order in which event objects are

stored in the eventsToProcess vector.

Example 17-2 shows the fetchEvents() method implementation for the

RMEventStore.

Example 17-2 The fetchEvents() method

public void fetchEvents() throws StatusChangeFailedException {

RMLogger.trace(CWConnectorUtil.LEVEL4, "Entering fetchEvents");

// find out how many events to process per poll (n)

int pollQuantity =

Integer.parseInt(CWConnectorUtil.getConfigProp("PollQuantity"));

// retrieve (n) number of ready for poll events from the event table

Vector fetchedEvents =

fetchEvents(

pollQuantity,

CWConnectorEventStatusConstants.READY_FOR_POLL);

// pass the vector of event objects to setEventsToProcess()

setEventsToProcess(fetchedEvents);

RMLogger.trace(CWConnectorUtil.LEVEL4, "Exiting fetchEvents");

}

Important: The fetchEvents() method is an abstract method. Therefore, the

event-store class must implement this method to provide the ability to fetch

READY_FOR_POLL events from the event store.

282 WebSphere Business Integration Adapters

The fetchEvents() method uses the private fetchEvents (pollQuantity, status)

method, as shown in Example 17-3.

Example 17-3 The private fetchEvents(pollQuantity, status) method

private Vector fetchEvents(int pollQuantity, int status)

throws StatusChangeFailedException {

RMLogger.trace(RMLogger.LEVEL4, "Entering fetchEvents(int, int)");

Vector fetchedEvents = new Vector();

// obtain connection from connection pool

RMServerRMIInterface connection;

try {

connection = (RMServerRMIInterface) connectionPool.getConnection();

} catch (Exception e) {

CWConnectorExceptionObject c = new CWConnectorExceptionObject();

c.setMsg("Unable to obtain connection to the application");

c.setStatus(CWConnectorConstant.APPRESPONSETIMEOUT);

throw new StatusChangeFailedException(c);

}

// retrieve <pollQuantity> number of <status> events from the event table

try {

// for each event retrived...

String eventId = "0";

boolean otherEvents = true;

int eventRetrieved = 0;

while (otherEvents && eventRetrieved < pollQuantity) {

//get the RMDataImplementation object

RMDataImplementation inpDataImpl =

getRMDataImplementationInstance(eventId, status);

//...retrieve the object

try {

RMDataImplementation outDataImpl =

(RMDataImplementation) connection.retrieveObject(

inpDataImpl);

// ...create a CWConnectorEvent object...

CWConnectorEvent aEvent =

getEventFromRMDataImplementation(outDataImpl);

//...save the key for the next event to retrieve...

eventId = aEvent.getEventID();

// ... and add it to the vector of fetched events

fetchedEvents.addElement(aEvent);

eventRetrieved++;

} catch (RemoteException e) { //no other events to retrieve

otherEvents = false;