RxJava instead of AsyncTask?

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The full power of RxJava is visible when you use it on Java 8, preferably with a library like Retrofit. It allows you to trivially chain operations together, with full control of error handling. For example, consider the following code given id: an int that specifies the order and apiClient: a Retrofit client for the order management microservice:

apiClient
.getOrder(id)
.subscribeOn(Schedulers.io())
.flatMapIterable(Order::getLineItems)
.flatMap(lineItem ->
    apiClient.getProduct(lineItem.getProductId())
             .subscribeOn(Schedulers.io())
             .map(product -> product.getCurrentPrice() * lineItem.getCount()),
    5)
.reduce((a,b)->a+b)
.retryWhen((e, count) -> count<2 && (e instanceof RetrofitError))
.onErrorReturn(e -> -1)
.subscribe(System.out::println);

This will asynchronously calculate the total price of an order, with the following properties:

  • at most 5 requests against the API in flight at any one time (and you can tweak the IO scheduler to have a hard cap for all requests, not just for a single observable chain)
  • up to 2 retries in case of network errors
  • -1 in case of failure (an antipattern TBH, but that’s an other discussion)

Also, IMO the .subscribeOn(Schedulers.io()) after each network call should be implicit – you can do that by modifying how you create the Retrofit client. Not bad for 11+2 lines of code, even if it’s more backend-ish than Android-ish.

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