How to use Observable.fromCallable() with a checked Exception?

Question

Observable.fromCallable() is great for converting a single function into an Observable. But how do you handle checked exceptions that might be thrown by the functio

Answer 1

You could also do this to return checked exceptions:

return Observable.fromCallable(() -> {
  sharedPreferences.edit()
          .putString(DB_COMPANY, LoganSquare.serialize(
                  CompanyDBTransformation.get(user.getCompany())
          ))
          .apply();
  return user;
  }).onErrorResumeNext(
            throwable -> Observable.error(new CompanySerializationException(throwable))
    );

So here I'm serializing taking the IOException risk, and I'm giving back a more descriptive description.

Answer 2

Rather than using a Func0 with Observable.fromCallable(), use Callable. For example:

Observable.fromCallable(new Callable<File>() {
    @Override
    public File call() throws Exception {
        return downloadFileFromNetwork();
    }
}

Since Callable's method call() throws Exception, you don't have to wrap your function in a try-catch! This must be what the lambda is using under the hood.