Spring Reactive Cassandra Kotlin Example

Spring Boot example with Spring Data Cassandra Reactive using Kotlin as programming language.

What is reactive streams and programming?

Reactive Streams is an initiative to provide a standard for asynchronous stream processing with non-blocking back pressure. — http://www.reactive-streams.org

Reactive programming is an asynchronous programming paradigm concerned with data streams and the propagation of change. This means that it becomes possible to express static (e.g. arrays) or dynamic (e.g. event emitters) data streams with ease via the employed programming language(s). — https://en.wikipedia.org/wiki/Reactive_programming

Setup

Make sure you have Cassandra running locally. You can download the distribution or use Docker:

docker run --name cassandra-db -d -p 9042:9042 cassandra

You need to create a cassandra keyspace with cqslh.

# qlsh --cqlversion=3.4.4
cqlsh> create KEYSPACE avthart with replication={'class':'SimpleStrategy', 'replication_factor':1};

You can configure the keyspace name with spring.data.cassandra.keyspace-name

Run

Start app using spring-boot maven plugin:

mvn spring-boot:run

Retrieve tasks using Server-Sent Events with httpie. The events are delayed with 500 ms because delayElements(...) is added to the Flux response, see code.

http -S :8080/tasks Accept:text/event-stream

Or retrieve as application/json:

http :8080/tasks

References

• https://docs.spring.io/spring/docs/current/spring-framework-reference/web-reactive.html#spring-webflux
• https://docs.spring.io/spring-data/cassandra/docs/current/reference/html/#cassandra.reactive
• https://projectreactor.io/