Messaging in Java is done using the JMS standard from JEE.
For messaging you need to choose a JMS provider such as:
-
Oracle Advanced Queuing (esp. if you already use Oracle RDBMS)
As a receiver of messages is receiving data from other systems it is located in the service-layer.
A JmsListener is a class listening and consuming JMS messages. It should carry the suffix JmsListener and implement the MessageListener interface or have its listener method annotated with @JmsListener. This is illustrated by the following example:
@Named
@Transactional
public class BookingJmsListener /* implements MessageListener */ {
@Inject
private Bookingmanagement bookingmanagement;
@Inject
private MessageConverter messageConverter;
@JmsListener(destination = "BOOKING_QUEUE", containerFactory = "jmsListenerContainerFactory")
public void onMessage(Message message) {
try {
BookingTo bookingTo = (BookingTo) this.messageConverter.fromMessage(message);
this.bookingmanagement.importBooking(bookingTo);
} catch (MessageConversionException | JMSException e) {
throw new InvalidMessageException(message);
}
}
}The sending of JMS messages is considered as any other sending of data like kafka messages or RPC calls via REST using service-client, gRPC, etc. This will typically happen directly from a use-case in the logic-layer. However, the technical complexity of the communication and protocols itself shall be hidden from the use-case and not be part of the logic layer. With spring we can simply use JmsTemplate to do that.