Spring Listener for MongoDB data insertion

Question

I have a requirement where I need to display data inserted into a particular MongoDB collection onto a User's dashboard in real time. Please note data maybe inserted by this user or other users. The dashboard is part of a Spring MVC web-application. The MongoDB data-layer is written in Spring Data.

I intend to use Server-sent events approach to push the newly inserted data to the dashboard. I am looking for an efficient way to listen to data insertion using Spring. I am even open to a non-Spring approach to implement the Listener that will eventually talk to my Spring SSE emitter.

Answer 1

If all the save goes through your spring-data layer, then you can make use of Mongo Listener Life cycle events docs.

@Component
public class MongoListener extends AbstractMongoEventListener<Account> 
{

    @Override
    public void onAfterSave(AfterSaveEvent<E> event) {

            if (LOG.isDebugEnabled()) {
                LOG.debug("onAfterSave({}, {})", event.getSource(), event.getDocument());
            }
        }
}

If not you would have to read mongo oplog and process or create a capped collection and use tailable cursors.
here is a sample project using tailable cursors.

Answer 2

You can do it via OpLog collection and Tailable Cursors in MongoDB. For example, get MongoDB OpLog Collection by using flags QUERYOPTION_TAILABLE | QUERYOPTION_AWAITDATA via your MongoDB framework (for example MongoDB Java Driver) and do the following query

MongoCursor<> cursor = db.getCollection('oplog.rs').find({ns:"collectionName", op:"i"})

where "collectionName" is the name of your collection and "i" is insert operation. After receiving events from the cursor you can send the events into a shared stream.

Unfortunately, I'm not familiar with Spring Data to provide an example for this, but the approach should be the same.