Patterns: Implementing Self-Service in an SOA Environment

328 Patterns: Implementing Self-Service in an SOA Environment

}

catch (Exception e) {

e.printStackTrace();

throw new MessageContextException();

}

return true;

}

}

10.6.2 Create the Aggregator mediation

This mediation is associated with the reply queue destination. When an incoming

message has the delivery type All, the request is sent to both the HomeDelivery

and the BusinessDelivery services. The reverse routing path is modified to new

reply queue destination. The response from both the messages is sent to this

reply queue destination where the Aggregator mediation is invoked. The

mediation aggregates the responses from both services into one response and

sends it back to the client.

The following are the steps to create the aggregator mediation:

1. Build the code:

a. Create a simple project called Aggregator.

b. Right-click the Aggregator project and select Add → Others → Java

Class. Name the class AggregatorMediation.

c. Implement the MediationHandler interface and add the code required for

aggregating the responses in the handle method (see “Aggregator code”

on page 329).

d. Create a JAR file from the package and call it Aggregator.jar.

2. Create the mediation EJB:

a. Create an EJB project called AggregatorEJB with an EAR file name of

AggregatorEJBEAR.

b. Drag and drop Aggregator.jar to the Utility JARS folder in

AggregatorEJBEAR.

3. Define the mediation handler in the EJB deployment descriptor:

a. Expand the AggregatorEJB project in the navigator and double-click

Deployment Descriptor.

b. Select the Mediation Handler tab.

Chapter 10. Web services scenario 329

c. Click Add and enter AggregatorHandler as the name. Enter

myPackage.AggregatorMediation as the handler class.

d. Save the descriptor.

Aggregator code

The handle() method (Example 10-8) is responsible for the message handling

and aggregation of the response messages, and sending the aggregated

response back to the original requester. The handle() method is invoked by the

arrival of a message on the queue that it has been configured to mediate,

DeliveryResponseDestination.

The handle() method casts the message context to an SIMessageContext and

retrieves the forward routing path for the message.

Example 10-8 AggregatorMediation code part 1

public class AggregatorMediation implements MediationHandler {

public boolean handle(MessageContext context) throws MessageContextException {

SIMessageContext ctx =(SIMessageContext)context;

String busName = ctx.getSession().getBusName();

SIMessage message = ctx.getSIMessage();

List frp = message.getForwardRoutingPath();

SIMediationSession session = ctx.getSession();

SIMessage otherMessage=null;

SIDestinationAddressFactory factory =

SIDestinationAddressFactory.getInstance();

Next (Example 10-9), it retrieves the name of a temporary storage queue it will

use to hold received messages. The code checks to see if it can receive a

message from the temporary queue. If no message is there, then the message

that has arrived on the mediated queue is the first response. If it is the first

response, the forward routing path is set to the temporary queue and the

message is stored there.

Example 10-9 AggregatorMediation code part 2

try {

otherMessage = session.receive((String)context.getProperty("TempDataDestination"));

if (otherMessage == null)

Note: The entire source code for the aggregator mediation can be seen by

downloading the sample application. The code is in the Aggregator.jar file in

the AggregatorEJB project.

330 Patterns: Implementing Self-Service in an SOA Environment

{

SIDestinationAddress queue= factory.

createSIDestinationAddress((String)context.getProperty("TempDataDestination"),busName);

frp.clear();

frp.add(queue);

message.setForwardRoutingPath(frp);

}

If there is a message on the temporary queue, this response is the second

message (Example 10-10).

The first message (otherMessage) is retrieved from the temporary queue and the

account number information (getAccountReturn) is extracted. Next, the account

information is extracted from the second message (message). Then the two

responses are combined and written back into the current (second) message.

Example 10-10 AggregatorMediation code part 3

else

{

DataGraph graph = null;

try {

graph = otherMessage.getDataGraph();

DataObject rootNode = graph.getRootObject();

DataObject infoNode = rootNode.getDataObject("Info");

DataObject bodyNode = infoNode.getDataObject("body");

DataObject part1Node = bodyNode.getDataObject("parameters");

String ticker = part1Node.getString("getAccountReturn");

DataGraph graph1 = message.getDataGraph();

DataObject rootNode1 = graph1.getRootObject();

DataObject infoNode1 = rootNode1.getDataObject("Info");

DataObject bodyNode1 = infoNode1.getDataObject("body");

DataObject part1Node1 = bodyNode1.getDataObject("parameters");

String ticker1 = part1Node1.getString("getAccountReturn");

part1Node1.setString("getAccountReturn",

ticker+","+ticker1);

Lastly (Example 10-11), the forward routing path is changed so the response will

be sent back to the client.

Example 10-11 AggregatorMediation code part 4

String newDestination =

(String)context.getProperty("InboundServiceClientResponseDest");

SIDestinationAddress newAddress = factory.