Scala Rest API with akka-http

Introduction

In this tutorial we shall explore how we can use akka-http to create service with scala. Here we create CRUD service with akka actor and try to see how it work. 

Versions

Scala version: 2.13.1

SBT version: 1.3.4

Other dependencies - 

About the service/project

We’ll create two actors that communicate with each other to get the user data and user activity data. 

Data Classes

We need two data classes that keeps the user data and user activity data.

Repository

Repositories are used to fetch the data from the actual source of data. The actual source can be anything like another service or some database. We created `UserActivityRepository` that have only one method `queryHistoricalActivities` to fetch the user activity by `userId`.

Actors to get user data 

We need two actor classes for `UserDataActor` and `UserActivityActor`. `UserDataActor` received 4 types of methods `Get`, `Post`,`Put` and `Delete` to retrieve, create, update and delete the user data respectively.  Once a message received, User data will be sent to the sender asynchronously.

`UserActivityActor` retrieve the user active once it receives the message `Get` 

Routing Configuration

Now, we need to create routing details, to access the user details from rest endpoints. We needs following endpoints 

#1	GET /api/users/activity	Retrieve user and its activity details.
#2	POST /api/user	To create user data
#3	PUT /api/user	To update user data
#4	DELETE /api/user	To delete user data

Routing code looks like below -

We have two `implicit` parameters in the routing config `implicit val userDataActorRef: ActorRef` and `implicit val system: ActorSystem`. `userDataActorRef` is used to get the user data. Since user details is required to register `UserActivityActor` we use actor system and implicit parameter to register `UserActivityActor` when we have user information available.

Web Server
This class is used to create http server and bind the endpoints with the http server. 

Run Application

Compile the code using below command

sbt compile

Run the application

sbt run

Now go to terminal, and run below httpie scripts 

Github links

Full code is available here to to explore and fork. Feel free to do whatever you want. ;)

Conclusion

We have seen here it’s easy to create rest services with akka and scala. You can get more information at
akka-http official document