Rx Java Workshop

This repository has some use cases related to RxJava and four missions for the workshop.

FactoryMethods module has factory methods that are commonly used for creating Observable.

TypesOfObservable module has some Observable types.

Operators module has some operators with use cases.

ErrorHandling module has some error handling operators with use cases.

UtilityForJavaDay module has an application that builds with Spring Boot. The application offers a variety of services for speakers of Java Day İstanbul. For example, mailing, notifications about cheap flight and hotel information, etc. Our missions, except one, will be related to this application.

Backpressure module has some examples of backpressure handling. One of our missions will be related to this module.

Missions

In this workshop, we have four missions.

Mission 1

In the Spring Boot application, we use Elasticsearch as a cache. Therefore, we have a scheduler that responsible for keeping Elasticsearch synchronized with the database.

final List<Speaker> speakers = daoService.findAllChangeSpeakersByTime(lastQueryTime);
final BulkRequest bulkRequest = new BulkRequest();
speakers.stream().forEach(speaker -> {
    bulkRequest.add(new IndexRequest(INDEX).id(String.valueOf(speaker.getId()))
               .source(XContentType.JSON,"name", speaker.getName(),
               "title", speaker.getTitle(),
               "approve", speaker.isApprove(),
               "retracted", speaker.isRetracted(),
               "mail", speaker.getMail(),
               "updateTime", speaker.getUpdateTime()));
    });

Related to this case, our mission is to use real-time synchronization with subject object of Rx Java instead of periodical synchronization with Scheduler.

Mission 2

We would like to inform the speakers whose talks are not approved and we also want to be aware of unsuccessful sendings while doing this. For that need, we use the following code block.

final List<Pair<Speaker, Future<String>>> tasks = speakers
        .stream().map(speaker -> Pair.of(speaker, sendEmailAsync(speaker)))
        .collect(toList());

final List<Speaker> failures = tasks.stream()
        .flatMap(pair -> {
            try {
                Future<String> future = pair.getRight();
                future.get(1, TimeUnit.SECONDS);
                return Stream.empty();
            } catch (Exception e) {
                Speaker speaker = pair.getLeft();
                logger.warn("Failed to send {}", speaker, e);
                return Stream.of(speaker);
            }
        }).collect(toList());

Related to this case, our mission is to use Observable instead of Future.

Mission 3

Our speakers have several criteria for travel. For example, they are suitable for travel only certain days, some prefer to travel in sunny weather they also have limits for flight and accommodation costs, etc. We have three streams each is independent of the other they are weather, flight, and hotel.

Related to this case, our mission is to report flights and hotels that match the criteria and declared weather conditions by composing Observables.

Mission 4

We have an HTTP server and it's under load so we care about logging every request without bad affecting response time.

Related to this case, our mission is to create a Flowable that uses backpressure for HTTP requests and log each request.

Requirements

1. Bring your laptop

2. Install JDK 8 or later by your computer.

3. Because the UtilityForJavaDay module uses Elasticsearch you must have a running Elasticsearch Server. You can download current Elasticsrarch version here https://www.elastic.co/downloads/elasticsearch In other option is Docker. The following command starts the Elasticsearch Server with Docker.

docker run -d --rm --name elasticsearch \ 
--net esnetwork \
-p 9200:9200 -p 9300:9300 \
-e "discovery.type=single-node" \
elasticsearch:7.5.2

Solutions

The solutions of the missions will be pushed solutions branch on the workshop day.