Comparing Interaction Styles

The objective is to compare the way the code is written depending on the interaction style chosen.

We use Spring Boot and implement:

1. a very simple API to retrieve a list of courses that are stored in a CSV file,
2. a slightly more complex API to retrieve company information from the SEC:

Main Differences

Style	Controller return type	Service return type	Exception handling	Testing
Synchronous API	ResponseEntity<List<CourseRepresentation>>	List<Course>	try / catch & ResponseEntityExceptionHandler	MockMvc
Asynchronous API	CompletableFuture<ResponseEntity<List<CourseRepresentation>>>	CompletableFuture<List<Course>>	exceptionally & ResponseEntityExceptionHandler	MockMvc
Reactive API	ResponseEntity<Flux<CourseRepresentation>>	Flux<Course>		WebTestClient

Note that since there is no semantic difference between an empty list of courses and no list at all, the service return type is not wrapped in an Optional.

Structure

The project is structured as follows :

• Synchronous API
• Asynchronous API
• Reactive API

We decided to create a module per type, in part because of what is mentioned in the Spring Boot Reference Documentation:

Adding both spring-boot-starter-web and spring-boot-starter-webflux modules in your application results in Spring Boot auto-configuring Spring MVC, not WebFlux. ... You can still enforce your choice by setting the chosen application type to SpringApplication.setWebApplicationType(WebApplicationType.REACTIVE).

Pre-requisites

Software

The following should be installed locally :

• Java 16
• Maven 3.6 or later

Build

The project is built using Maven.

Run

Each module can be run in the same manner.

Here are the instructions for the api-sync module.

Command Line

• Build and package

mvn clean package

• Start the service

cd api-sync java --enable-preview -jar target/api-sync.jar

The server port is 9000 as specified in the application configuration.

• Access the API

curl -i 'http://localhost:9000/sync/courses?departmentCode=POL'

if you have json_pp, you can pretty print the result:

curl -X GET 'http://localhost:9000/sync/courses?departmentCode=POL' | json_pp

• Debug

If you need to debug the service, use the following command to start the service

java -Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket,address=8000,server=y,suspend=n -jar target/api-sync.jar

then connect a remote debugging session to port 8000

• Profile using Java Mission Control

Download Java Mission Control from here for OpenJDK or here for Oracle since it's not part of the JDK 11 anymore.

If you need to profile the service, use the following command to start the service

java -XX:+FlightRecorder -jar target/api-sync.jar

For offline profiling use

java -XX:+FlightRecorder -XX:StartFlightRecording=duration=200s,filename=flight.jfr -jar target/api-sync.jar

To Do

• Implement Reactive ( 204 when no courses + exception handling )
• Add Virtual Thread style
• Add an API with 2 parallel calls
• Add a database call and an API call
• Add a client using the JDK's HttpClient
• Add tests for error cases