This document summarizes a presentation on baking reactive behavior into Java EE applications. It discusses reactive support in Java EE 7, using Java 8 features like CompletableFuture with asynchronous APIs. It demonstrates passing CompletableFuture as a parameter to complete later. The presentation also covers concurrency utilities, a live demo of a reactive cargo tracker app, Payara Micro for application servers as JARs, and dynamic scaling. General advice is given to not over-engineer for full reactivity but leave doors open to gradual improvement.

1. Ondrej Mihályi
Payara Services
How to Bake Reactive Behavior
into your Java EE Applications

2. @OMihalyi
Agenda
➢
Reactive Support in JavaEE7
➢
Java 8 goodness on Reactive
Implementations
➢
Payara Micro Additions
➢
Live demo
➢
Q&A

3. @OMihalyi
Reactive Manifesto
ResponsiveResponsive
ElasticElastic ResilientResilient
Message DrivenMessage Driven

4. @OMihalyi
Traditional approach
Request started
→ external resource required (DB, WS, files)
→ request external resource
→ external resource is slow
WHAT DO WE DO?

5. @OMihalyi
Traditional approach
WE SIMPLY WAIT…

6. @OMihalyi
Traditional approach
WE SIMPLY WAIT…
• Simple
• Thread-safe
• Often Sufficient (when
waiting time is negligible)

7. @OMihalyi
But…

8. @OMihalyi
But…
•… if waiting is too long
 Thread resources are
wasted
 Processing may halt if all
threads waiting

9. @OMihalyi
Spawn a separate thread
• Idea:
- Blocking call in a new thread
- Do something while waiting
- Retrieve results
- Fail after timeout vs. block
infinitely
- java.util.concurrent.Future

10. @OMihalyi
Drawbacks…
• Complexity
 keep asking “Are you ready?”
• Requires one more thread
 blocked while waiting

11. @OMihalyi
Finish in a new thread!
•Idea:
− Blocking call in another thread
− Transfer context to another thread
− No need to wait for the
blocking call
− But new thread may still be
blocked…

12. @OMihalyi
…and asynchronous calls
• Idea:
− Provide a callback
− Call finishes immediately
− Callback called in a new thread
− Finish request in the callback
− No need to wait at all
− But, is it possible?

13. @OMihalyi
Asynchronous API in Java EE
• Async Servlet request completion
• Async JAX-RS request completion
• Async JAX-RS client
• Async IO in Servlet
• Async EJB calls
• Managed Executors
• WebSockets

14. @OMihalyi
Async API Example
• JAX-RS AsyncResponse @Suspended
@GET
void get(@Suspended
AsyncResponse response)
…
response.resume("OK");

15. @OMihalyi
Async API Example
• JAX-RS async client
resourceTarget
.request(MediaType.TEXT_PLAIN)
.async()
.get(
new InvocationCallback() …

16. @OMihalyi
Java EE + Java 8
•Future → CompletableFuture ?
− No, not compatible
•Callbacks → CompletableFuture
− callback triggers cf.complete()
•Pass CF as additional parameter
to complete it later

17. @OMihalyi
Pass CF as additional parameter
cf = new CompletableFuture<...>();
webtarget.async()
.get(new InvocationCallback() {
… cf.complete(result); …
});
cf.thenAccept(result -> {
/* Do something after */ });

18. @OMihalyi
CompletableFuture
− Chain callbacks (like promises)
●
thenRun(), thenApply(), …
●
thenCompose()
− Complete execution in any thread
●
compFuture.complete()

19. @OMihalyi
Concurrency utilities
ctxSvc.createContextualProxy(
() -> {…wrapped code…},Runnable.class})
• Requests span multiple threads
• Context must be retained
• Managed threads (ExecutorService)
• ContextService for non-managed

20. @OMihalyi
Live Demo
• Revisit famous cargo-tracker in a reactive way
Available at:
https://github.com/OndrejM-demonstrations/Reactive-CargoTracker

21. @OMihalyi
●
Other parts of being Reactive
•We’ve shown responsive API
•The other 3 reactive concepts:
−Resilience
−Messaging
−Elasticity

22. @OMihalyi
Payara Micro
• Application server as executable JAR
• Runs WAR apps from command line
• automatic and elastic clustering
→ spawn many micro services dynamically
→ replication using distributed cache
→ shared 60MB runtime, 40MB in heap
www.payara.fish

23. @OMihalyi
•Simple messaging and caching
@Inject @Outbound
Event<MyMsg> ev;
// handle in different JVM
void handle(@Observes
@Inbound MyMsg ev) {
… }
Payara Micro Event Bus
- events triggered on all nodes
- Asynchronous micro services
- No need for service registry
- On top of CDI events
JCache API
• Standard Java API for caching
• Distributed cache
Simple messaging and caching

24. @OMihalyi
Dynamic scaling
• Just run repeatedly
• binds to a free port to avoid port collisions
• All instances autoconnect to a cluster
− Even across network (multicast)
java -jar payara-micro.jar
--deploy app.war
--autoBindHttp

25. @OMihalyi
Live Demo
• Enhancements to the Cargo Tracker app using
Payara Micro features

26. @OMihalyi
• Fully reactive comes at a greater cost
− Dealing with threads, hard to track
origin, communication overhead
• Don’t over-engineer, but leave doors
open
• Java EE enables gradual
improvement
General advice

27. @OMihalyi
Questions?
Thank you