title: Project Reactor's Flux get failed item during handling error
body: <p>I need to handle <code>Flux</code> stream error and for that I need to know what exactly item is failed. Seems method <code>doOnError</code> should be appropriate for handling error, but with that I can only get exception and not a failed item. Is there any way to get both failed item and exception?</p>
  
  <pre><code>private void testFluxIterableFlow() {
      Flux.fromIterable(Arrays.asList(1, 2, 3, 4, 5))
              .map(this::process)
              .doOnError(ex -&gt; {
                  ...
              })
              .doOnNext(processedValue -&gt; ...)
              .subscribe();
  }
  
  private String process(Integer value) {
      if (value == 4) {
          throw new RuntimeException("error...");
      }
      return "processed " + value;
  }
  </code></pre>
  
  <p>in this example, I need to receive failed item <code>4</code> and exception message in error handler.</p>