Throwing an exception on subscription in RxJava

Question

Consider the following code :

  public static void main(String[] args) {
    try {
        observableTesting();
    } catch (Exception ex) {
        System.out.println("Exception propagated : " + ex.getLocalizedMessage());
    }
}


private static void observableTesting() throws Exception{
    Observable.fromCallable(() -> { throw new Exception("TEST"); })
            .subscribe(
                    next -> {},
                    error ->
                    {
                        System.out.println("Error : " + error.getLocalizedMessage());
                        throw new Exception(error);
                    }

            );}

I would expect this to throw an exception and to propagate it to the calling function. This doesn't seem to produce the desirable effect.

As a workaround, I currently have to assign the error and throw it at the end of the function.

Are there any better ways to convert observable errors into exceptions?

Answer 1

It seem you're using rxjava-2. Under this version, the specification for errors state that all not handled Throwable will be delivered through either the Thread.UncaughtExceptionHandler installed on the system or the error handler installed via RxJavaPlugins.setErrorHandler(). If you're seeking to test the whether an observable throws or not, you can use TestObserver instead, as:

Observable
     .fromCallable(() -> { throw new Exception("TEST"); })
     .test()
     .assertSubscribed()
     .assertError(Exception.class);