- Java EE supports reactive applications through asynchronous APIs, non-blocking IO, and managed executors. CompletableFuture in Java 8 improves asynchronous programming. - Payara Micro enables reactive microservices through automatic clustering, distributed caching, and a lightweight event bus using CDI events. - While fully reactive approaches have high costs, Java EE leaves the door open for gradual improvements to reactivity through standards like JCache and by leveraging asynchronous capabilities.

1. How to bake reactive
behavior into your Java EE
applications
Ondrej Mihályi
@OMihalyi

2. @OMihalyi
AgendaAgenda
➢
What is a reactive app
➢
Support in Java EE 7
➢
Java 8 joins the game
➢
Payara Micro additions
➢
Live demo
➢
Common pitfalls

3. @OMihalyi
Ondrej
Mihályi
Web:
itblog.inginea.eu
Twitter:
Ondrej
Mihályi
Web:
itblog.inginea.eu
Twitter:
Payara suppor
engineer
Java EE developer
Java EE lecturer
Java blogger
Scrummaster

4. @OMihalyi
Reactive applicationReactive application

5. @OMihalyi
Possible in Enterprise?Possible in Enterprise?
New tools and frameworks
➔
High risks and costs
Fully reactive approach
➔
High cost of development
➔
Harder to avoid and track bugs
Advice → reactive where it’s worth
→ leave the door open for future

6. @OMihalyi
Java EE leaves the door openJava EE leaves the door open
Established and wide-spread
– Built with resilience in mind (Transactions)
– Messaging is first-class citizen (JMS)
Continuous improvements
– Asynchronous API, thread-management
– Scalability improvements (JCache)
– Portable CDI extensions

7. @OMihalyi
Traditional approachTraditional approach
Request started
→ external resource required (DB, WS, files)
→ request external resource
→ external resource is slow
→ what do we do?
We SIMPLY wait…

8. @OMihalyi
Traditional approachTraditional approach
We SIMPLY wait…
Simple
Thread-safe
Sufficient when waiting time is
negligible

9. @OMihalyi
Traditional approachTraditional approach
Blocking calls:
JDBC:
ResultSet rs =
stmt.executeQuery(q);

10. @OMihalyi
Traditional approachTraditional approach
Blocking calls:
JPA:
List r =
query.getResultList();
Servlet:
response.getWriter()
.print(s);

11. @OMihalyi
Traditional approachTraditional approach
Blocking design:
– Servlet filters
– Interceptors
– JSF lifecycle

12. @OMihalyi
Spawn a separate threadSpawn a separate thread
Idea:
– Blocking call in a new thread
– Do something while waiting
– Join the thread and retrieve results
– Fail after timeout vs. block infinitely

13. @OMihalyi
java.util.concurrent.Futurejava.util.concurrent.Future
Solution in Java world (since Java 5)
@Asynchronous methods since Java EE 6
– Solves the problem for fire-and-forget
– Still drawbacks when result needed
●
Complexity – keep asking “Are you ready?”
●
Requires one more thread
– blocked when nothing to do while waiting

14. @OMihalyi
@Asynchronous@Asynchronous
Any EJB method or all methods of an EJB
Executes in another thread in pool
Fire-and-forget with void result
Return result as a Future
– Future not efficient enough, we’ll improve later

15. @OMihalyi
@Asynchronous - Fire-and-
forget
@Asynchronous - Fire-and-
forget
@Asynchronous
void fireAndForget
(String message)
{
… // long-running task
}

16. @OMihalyi
Non-blocking API in Java EE 7Non-blocking API in Java EE 7
AsyncContext in Servlet (since 3.0, Java EE 6)
// get context for another thread
AsyncContext ctx =
req.startAsync();
AsyncContext
.getResponse()
.getOutputStream()…
ctx.complete();

17. @OMihalyi
Non-blocking API in Java EE 7Non-blocking API in Java EE 7
AsyncContext in Servlet
AsyncContext ctx =
req.startAsync();
AsyncContext // build response (in any thread)
.getResponse()
.getOutputStream()…
// finish (in new thread)
ctx.complete();

18. @OMihalyi
Non-blocking API in Java EE 7Non-blocking API in Java EE 7
AsyncContext in Servlet
– Requires to turn on async support
●
Using @WebServlet annotation
●
In web.xml descriptor
@WebServlet
(asyncSupported=true)

19. @OMihalyi
Non-blocking API in Java EE 7Non-blocking API in Java EE 7
Async IO in Servlet 3.1 (Java EE 7)
– Non-blocking reading of multi-part form
– Non-blocking writing of response body
Non-blocking IO in Java (NIO)
– to read HTML from files

20. @OMihalyi
Non-blocking APINon-blocking API
JAX-RS AsyncResponse
@Suspended@GET
void get(@Suspended
AsyncResponse r)
…
// in another thread
response.resume("OK");

21. @OMihalyi
Non-blocking APINon-blocking API
JAX-RS AsyncResponse
@Suspendedvoid get(@Suspended
AsyncResponse response)
…
// in another thread
response
.resume("OK");

22. @OMihalyi
Non-blocking APINon-blocking API
JAX-RS async client
resourceTarget
.request(MediaType.TEXT_PLAIN)
.async()
.get(new
InvocationCallback
() { … });

23. @OMihalyi
CDI events + @AsynchronousCDI events + @Asynchronous
CDI events decouple components
– one-way communication
– handlers triggered in the same thread
→ emitter is blocked
Handlers are asynchronous EJB methods
– triggered in anyther thread
→ emitter not blocked

24. @OMihalyi
@Inject
Event<MyEvent> ev;
…
ev.fire(new MyEvent());
…
@Asynchronous
void handle(@Observes
MyEvent ev) { … }

25. @OMihalyi
Summary of approachesSummary of approaches
Traditional blocking API
– Easy to use, halts execution until finished
→→

26. @OMihalyi
Summary of approachesSummary of approaches
Traditional blocking API
– Easy to use, halts execution until finished
Asynchronous call with Future
– not blocking, +1 thread
Asynchronous call with callback
– Not blocking, 1 thread at a time, callback hell

27. @OMihalyi
Java 8Java 8
CompletableFuture (CompletionStage)
– Chain callbacks (like promises)
– Execute in the same or another thread
● thenRun(), thenRunAsync(), …
● thenCompose(),…
– Complete execution in any thread at any time
● completableFuture.complete()
thenComposeAsync()

28. @OMihalyi
thenComposeAsync()thenComposeAsync()
CompletableFuture<String>
cf = new
CompletableFuture<>();
…
cf.thenComposeAsync( r ->
return callThatReturnsCF(r);
), executor)
…
cf.complete(awaitResult())

29. @OMihalyi
thenComposeAsync()thenComposeAsync()
…
cf.thenComposeAsync(
r -> returnsCF(r)
), executor)
.thenComposeAsync(…
…
cf.complete(r);

30. @OMihalyi
Java EE + Java 8Java EE + Java 8
Future → CompletableFuture ?
– No, not compatible
Callbacks → CompletableFuture
– callback triggers cf.complete()
Pass CF as additional parameter

31. @OMihalyi
Pass CF as additional parameterPass CF as additional parameter
void asyncCall(CompletableFuture cf) {
… cf.complete(result);
}
… cf = new CompletableFuture<String>();
asyncCall(cf);
cf.thenComposeAsync(
result -> … , executor);

32. @OMihalyi
Use managed executorsUse managed executors
CF async methods use ForkJoinPool
– Not managed by Java EE
Always use a managed executor
@Resource
ManagedExecutorService
executor;

33. @OMihalyi
Other parts of being ReactiveOther parts of being Reactive
We’ve shown responsive API
The other 3 reactive concepts:
– Resilience
– Messaging
– Elasticity

34. @OMihalyi
ResilienceResilience
Responsive in the face of failures
Server clusters and transaction isolation
Load balancer in front
Microservices (embedded server)
… reduce single points of failure

35. @OMihalyi
Payara MicroPayara 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
→ → V

36. @OMihalyi
Messaging in Java EEMessaging in Java EE
JMS – traditional solution
– Topics, Queues, Persistence,
Transactional, Repeated delivery
– Simplified API in Java EE 7
●
some bioler-plate still necessary

37. @OMihalyi
Why not make it even simpler?
@Inject @Outbound
Event<MyMsg> ev;
// handle in different JVM
void handle(@Observes
@Inbound MyMsg ev) {
… }

38. @OMihalyi
Payara Micro event busPayara Micro event bus
events handled by any distributed node
– Asynchronous (reactive) micro services
– No need for service registry
On top of CDI events, just 2 qualifiers
– @Outbound event, @Inbound observer
Uses Hazelcast distributed executor

39. @OMihalyi
Elasticity in Java EEElasticity in Java EE
Weakest point of Java EE specs
– Clusters do not scale dynamically
Many provider-specific solutions
JCache JSR – targets Java EE 8

40. @OMihalyi
JCacheJCache
Standard Java API for caching
Distributed
API and CDI binding
Supported by many cache providers
Built in to Payara Server and Payara Micro

41. @OMihalyi
@Inject MyCache cache;
…
value = cache.get(key);
…
@CacheResult
Object get(
@CacheKey Object key)
JCache CDI bindingJCache CDI binding

42. @OMihalyi
mycache.put(key, value);
…
@CachePut
void put(
@CacheKey Object key,
@CacheValue Object v)
{ // body can be empty }
JCache CDI bindingJCache CDI binding

43. @OMihalyi
Dynamic scalingDynamic 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.java
--deploy app.war
--autoBindHttp

44. @OMihalyi
Payara Micro examplePayara Micro example
web service on single node, computation
service scaled to multiple nodes
– Web service fires an @Outbound event
– Computation started on a computation node
●
Synchronisation using Jcache API
– An event with result fired
– Observed by web service and returned

45. @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 adviceGeneral advice

46. @OMihalyi
Questions?Questions?
Thank you