Handling errors

When dealing with errors in RxJava, you should be aware that they terminate the Observable chain of actions. Much like with your normal procedural code, once you are in the catch block, you can't go back to the code that has thrown the exception. You can execute some backup logic though and use it instead of failing the program. The return*, retry*, and resume* operators do something similar.

The return and resume operators

The onErrorReturn operator can be used in order to prevent the Subscriber instance's onError from being called. Instead, it will emit one last item and complete. Here is an example:

Observable<String> numbers = Observable
  .just("1", "2", "three", "4", "5")
  .map(Integer::parseInt)
  .onErrorReturn(e -> -1);
  subscribePrint(numbers, "Error returned");

The Integer::parseInt method will succeed in converting the strings 1 and 2 to Integer values, but it will fail on three with a NumberFormatException exception. This exception will be passed to the...