Red Hat Application Server, Manual

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Chapter 9. Developing Message-Driven Beans 125
Figure 9-1. Example Architecture
There are two Message-Driven Beans in this example:
•
$JONAS_ROOT/examples/src/mdb/sampleappli/StockHandlerBean is a Message-Driven Bean lis-
tening to a topic and receiving Map messages. The
onMessage
method runs in the scope of a
transaction started by the container. It sends a Text message on a Queue (OrdersQueue) and up-
dates a Stock element by decreasing the stock quantity. If the stock quantity becomes negative, an
exception is received and the current transaction is marked for rollback.
•
$JONAS_ROOT/examples/src/mdb/sampleappli/OrderBean is another Message-Driven Bean lis-
tening on the OrdersQueue Queue. On receipt of a Text message on this queue, it writes the corre-
sponding String as a new line in a file (
Order.txt
).
The example also includes a CMP Entity Bean $JONAS_ROOT/examples/src/mdb/sampleappli/Stock
that handles a stock table.
A Stock item is composed of a Stockid (String), which is the primary key, and a Quantity (int). The
method
decreaseQuantity(int qty)
decreases the quantity for the corresponding stockid, but
can throw a RemoteException
Negative stock.
The JMS Client application
SampleAppliClient
sends several messages on
StockHandlerTopic
(see $JONAS_ROOT/examples/src/mdb/sampleappli/SampleAppliClient.java). It uses Map
messages with three fields:
CustomerId
,
ProductId
, and
Quantity
. Before sending
messages, this client calls the EnvBean for creating the
StockTable
in the database