Question

We have ActiveMQ onto which the events that happen in the system are published. The project involves users adding entities to their watch-list and whenever there are events on those entities I would like an email to be sent out to the interested participants.

The use-case roughly translates to some one expressing an interest in a product information page on the catalog and an email being sent whenever any activity happens on that product (price goes down, there is a positive review etc.,). I had modelled this interaction as a Camel route.

So, for example, if the user says email me whenever this product’s rating equals 5, then the following route would be added to the camel context:

from("activemq:topic:events.product.save").filter().xpath("/object[<object id>]/rating").isEqualTo("5").to("email:<user's email>")

Similarly if the user wants to be notified whenever there is a new comment on a product, another route would be created and so on. This could potentially, end up creating thousands of routes as each user starts adding their watches of interest.

Some questions that I have are:

• Is this an acceptable way of creating dynamic routes? One option I am considering is to use recipient lists. But I haven’t been able to come up with a solution that would make it elegant to route messages to the bean that would return the recipient list. For example for the case explained above would the bean have a bunch of if-else to see which recipient list to return?

• The camelcontext has a method to load routes from a xml file but no method to persist the existing routes. What would be simplest (and efficient) way to persist these dynamically created routes? This thread in the camel-users list sums up my request.

Answer 1

Given the dynamic nature of your subscription requirements, you should use a database to store the information rather than trying to create dynamic routes. This is a much more scalable/appropriate use of technology…

Then you can only need a single static route or a POJO consumer (see below) that can process the product update messages using a simple POJO bean (bean-binding can help, etc). The POJO bean would then be responsible for querying the database to find all “interested” users and send an email using camel-mail

public class NotificationBean {

    @Consume(uri="activemq:topic:events.product.save")
    public void onUpdate(@XPath("/object/id") String id, 
                         @XPath("/object/rating") String rating) {
        //query database for subscriptions for this product ID/rating, etc.
        //for each interested subscriber
            //send email (camel-mail, etc)
    }

    public void addSubscription(String productID, Integer rating, String email) {
        //create/update subscription entry in database, etc...
    }
}