Best way to limit parallel request in a @RestController method

Question

Considering the following code:

@RestController
@RequestMapping("/requestLimit")
public class TestController {

    @Autowired
    private TestService service;

    @GetMapping("/max3")
    public String max3requests() {
        return service.call();
    }
}

@Service
public class TestService {

    public String call() {
        //some business logic here
        return response;
    }
}

What i want to accomplish is that if the method call from the TestService is being executed by 3 threads at the same time, the next execution generate a response with a HttpStatus.TOO_MANY_REQUESTS code.

You have to keep a Atomic variable and increment in your controller class. Increment it in your method and check if it exceeds 3 and if yes return else proceed — pvpkiran
– pvpkiran, Commented Aug 30, 2018 at 14:03
Thanks @pvpkiran, with your recomendation I managed to propose an answer — Julio Villane
– Julio Villane, Commented Aug 30, 2018 at 14:40

Julio Villane · Accepted Answer · 2018-08-30 14:39:52Z

Thanks to @pvpkiran comment I managed to code this:

@RestController
@RequestMapping("/requestLimit")
public class TestController {

    private final AtomicInteger counter = new AtomicInteger(0);

    @Autowired
    private TestService service;

    @GetMapping("/max3")
    public String max3requests() {
        while(true) {
            int existingValue = counter.get();
            if(existingValue >= 3){
                throw new TestExceedRequestLimitException();
            }
            int newValue = existingValue + 1;
            if(counter.compareAndSet(existingValue, newValue)) {
                return service.call();
            }
        }
    }
}

@Service
public class TestService {

    public String call() {
        //some business logic here
        return response;
    }
}

With the corresponding exception definition:

@ResponseStatus(HttpStatus.TOO_MANY_REQUESTS)
public class TestExceedRequestLimitException extends RuntimeException{ }

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