Step 2: Exploring the app

The app is a simple microservice based on Spring Boot for rating conference talks. It provides an API to track the ratings of the talks in real time.

Storage

SQL database with the talks

When a rating is submitted, we must verify that the talk for the given ID is present in our database.

Our database of choice is PostgreSQL, accessed with Spring JDBC.

Check com.example.demo.repository.TalksRepository.

Redis

We store the ratings in Redis database with Spring Data Redis.

Check com.example.demo.repository.RatingsRepository.

Kafka

We use ES/CQRS to materialize the events into the state. Kafka acts as a broker and we use Spring Kafka.

Check com.example.demo.streams.RatingsListener.

API

The API is a Spring Web REST controller (com.example.demo.api.RatingsController) and exposes two endpoints:

• POST /ratings { "talkId": ?, "value": 1-5 } to add a rating for a talk

• GET /ratings?talkId=? to get the histogram of ratings of the given talk