How to implement HttpRequestRetryHandler with Exponential Backoff?

Question

I wish to implement a HttpRequestRetryHandler for a HttpClient in case the request fails first time.

I also wish to implement Exponential backoff for subsequent retries. Mathematically it can be implemented as

E(c) = 1/2(2 power (c) -1)

but I am struggling for quite some time now to implement it in the code with HttpRequestRetryHandler.

Answer 1

HttpRequestRetryHandler doesn't allow you that level of control; if you want to do something very specific like that, I'd recommend implementing something like a Handler where you can post Runnables to be executed with a delay, using for example Handler.postDelayed() with increasing delays as per your formula.

Handler mHandler = new Handler();
int mDelay = INITIAL_DELAY;

// try request
mHandler.postDelayed(mDelay, new Runnable() {
   public void run() {
      // try your request here; if it fails, then repost:
      if (failed) {
          mDelay *= 2;  // or as per your formula
          mHandler.postDelayed(mDelay, this);
      }
      else {
          // success!
      }
   }
});

Answer 2

Here is a good framework with backoff algorithms - https://github.com/rholder/guava-retrying