Rate limiting outgoing requests in Java but with a dynamic rate

Question

I am building an application which includes a scraper of a public API. I want to limit the rate of my requests but not with a fixed rate, but a dynamic randomised rate which changes in-between requests and falls in a certain range, ie I can set the minimum and maximum delay between requests.

I also don't want to block the current thread.

I've researched Guava Ratelimiter, RatelimitJ and Token bucket algorithm but looking at the docs, I don't see how any of those things can achieve what I want.

Example of the desired effect on my requests given a rate limit range of 250-350ms:

• Make request #1
• wait 321ms
• Make request #2
• wait 259ms
• Make request #3
• wait 337ms
• ...

Answer 1

You don't need to look outside the JDK. You can use java.util.concurrent.ScheduledExecutorService to make the call after a defined delay and in a separate thread. To use this you will need to implement java.util.concurrent.Callable or java.lang.Runnable for the code that does the API call.

    ScheduledExecutorService service = Executors.newScheduledThreadPool(1);
    Callable apiCaller = ...;

To make the call so that it runs after a defined delay you submit it as follows:

    service.schedule(apiCaller, delay, TimeUnit.MILLISECONDS);

To get a random delay you just need to use java.util.Random .

        Random random = new Random();

Random can provide you with a bounded integer. So if you pass it the acceptable range and then add then add the minimum you will get a random number between the minimum and maximum you want.

   int minimumDelay = 250;
   int maximumDelay = 350;       
   int delay = random.nextInt(maximumDelay - minimumDelay) + minimumDelay;