Spring Reactive Programming - “监听”数据存储区的更改

Question

When using Spring's new Reactive technology, is it possible to "listen" on a datastore for any changes, so you get a callback for any changes on it? Imagine being able to suscribe on a MongoDB repository, so a change in the database will trigger a given method?

Answer 1

Continuous queries depend on the used data store. I'm currently aware of three stores that are capable of such a feature:

• MongoDB (Capped collections and tailable cursors, supported via @Tailable in Spring Data Repositories)
• Redis (Using either Pub/Sub messaging or listening to keyspace notifications, not yet supported in a reactive way with Spring Data Redis, but you can build it yourself or submit a PR)
• Apache Geode (previously GemFire) that supports continuous queries (not yet supported in a reactive way with Spring Data for Apache Geode).

A reactive type is not required to emit a finite number of items per se. An infinite stream can be anything you want to listen to/process for a longer time. A messaging system (JMS) is a good example for a message listener for a traditional approach. You use a messaging system in the way to emit messages through the stream. This works in similar for the previously mentioned data stores.

For example, MongoDB can use tailable cursors on a capped collection and emit data on the stream. As soon as a client inserts a new document into the collection, the server emits the document to the client which pushes it through the stream.