How to implement Long Polling REST endpoint in Spring Boot app?

Question

Would you be so kind as to share any up-to-date manual or explain here how to implement a REST Long Polling endpoint with the latest Spring (Spring Boot)?

Everything that I've found by this time is quite out-dated and was issued a couple of years ago.

So, I've raised a question is Long Polling still a good approach? I know it's used in chess.com

Answer 1

For long pulling request you can use DeferredResult. when you return DeferredResult response, request thread will be free and this request handle by worker thread. Here is one example:

@GetMapping("/test")
    DeferredResult<String> test(){
        Long timeOutInMilliSec = 100000L;
        String timeOutResp = "Time Out.";
        DeferredResult<String> deferredResult = new DeferredResult<>(timeOutInMilliSec,timeOutResp);
        CompletableFuture.runAsync(()->{
            try {
                //Long pooling task;If task is not completed within 100 sec timeout response retrun for this request
                TimeUnit.SECONDS.sleep(10);
                //set result after completing task to return response to client
                deferredResult.setResult("Task Finished");
            }catch (Exception ex){
            }
        });
        return deferredResult;
    }

In this request give response after waiting 10 sec. if you wait more than 100 sec you will get timeout response.

Look at this.