Switch to Spring for the REST API

[marcomicera]

As far as the REST API is concerned, there are still a few issues:

• A couple of timeout Few JOOQ queries (REST API) cause Jetty's idleTimeout #86
• CDI not working (needed for unit testing) REST API unit tests #87
• Unsupported concurrent requests Make sure the REST API handles concurrent requests #93

All (or part of) these problems could be solved together by switching from RESTeasy to Spring (especially for Spring DI).

This change would also affect integration tests #89 and Dockerization #101.

[gousiosg]

Could you please explain how / why the problems you describe will be solved with Spring?

[marcomicera]

Could you please explain how / why the problems you describe will be solved with Spring?

Sure, sorry for my brevity.

1. First things first: the Spring DI. Spring has some dedicated annotations like @Autowired and @Service that already allowed me to have a fully-functional CDI system. This simplifies unit testing a lot REST API unit tests #87.
2. I already noticed that this Spring version of the REST API doesn't suffer from most of the timeouts we had before. I think this is due to Spring's embedded Tomcat Servlet container. I didn't manage to find out why Jetty caused timeouts, so a very dumb solution would be to just get rid of it.
3. For concurrency, I think this is going to be handled by Spring & Tomcat. I didn't find any simple solution for Jetty rather than spawning threads manually Make sure the REST API handles concurrent requests #93 (comment). I think this could be achieved with a simple server.tomcat.max-threads=400 with the Spring's embedded Tomcat. There seem to be lots of other tweaks as well for Spring.

[marcomicera]

@ilyagrishkov @MihhailSokolov do I have to keep Main.java and RestAPIPlugin.java that implements the PF4J Plugin interface and DBConnector?
It's a bit complicated to launch Spring through such classes.

I'd just use:

@SpringBootApplication
public class RestApplication {

    public static void main(String[] args) {
        SpringApplication.run(RestApplication.class, args);
    }
}

With a Spring @Component that connects to the KnowledgeBase at the beginning:

@Component
public class KnowledgeBaseConnector {

    @PostConstruct
    public void connectToKnowledgeBase() { /* ... */ }
}

So instead of launching it with mvn exec:java it would be: mvn spring-boot:run.
So technically, not a PF4J plugin anymore: is it ok?

[marcomicera]

Done in #123.