JAX-RS 2.1 SSE Client API example using Glassfish 5 on Docker

Along with the Server API for SSE, JAX-RS 2.1 (part of Java EE 8) also has an equivalent client side API

Here is a quick peek – you can grab the project from Github

@Singleton
@Startup
public class ProgrammaticSSEClient {
Client sseClient;
WebTarget target;
@Resource
TimerService tsvc;
@PostConstruct
public void init() {
this.sseClient = ClientBuilder.newClient();
this.target = this.sseClient.target("https://sse.now.sh");
tsvc.createSingleActionTimer(15000, null);
System.out.println("SSE client timer created");
eventSource = SseEventSource.target(target).build();
System.out.println("SSE Event source created……..");
}
SseEventSource eventSource;
@Timeout
public void client() {
System.out.println("SSE Client triggered in thread "+ Thread.currentThread().getName());
try {
eventSource.register((sseEvent)
> {
System.out.println("Events received in thread " + Thread.currentThread().getName());
System.out.println("SSE event recieved —– " + sseEvent.readData());
},
(e) > e.printStackTrace());
eventSource.open();
System.out.println("Source open ????? " + eventSource.isOpen());
} catch (Exception e) {
e.printStackTrace();
}
}
@PreDestroy
public void close() {
eventSource.close();
System.out.println("Closed SSE Event source..");
sseClient.close();
System.out.println("Closed JAX-RS client..");
}
}

To summarize

  • we use a @Singleton EJB with @Startup
  • during initialization
    • create a single action (one time) Timer  i.e. @PostConstruct
    • and instantiate the SSEEventSource – its a public SSE source
  • when the timer expires, the @Timeout annotated method gets triggered
    • opens the SSE connection
    • prints them out – this action is registered as a callback (written as a Java 8 lamda in this case)
  • Execution thread pool(s) – notice this in the logs
    • the timer itself is triggered in the EJB thread pool
    • SSE event callbacks are executed in the ManagedExecutorService thread pool (thanks to Java EE Concurrency Utilities)

sse-client-output.jpg

To run using Docker

Refer README

Further reading

Cheers!

About Abhishek

Loves Go, NoSQL DBs and messaging systems
This entry was posted in Java EE and tagged , , , , , , , . Bookmark the permalink.

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