The event bus is a fundamental tool for articulating event processing in Vert.x, but there is more to it! Event-bus services are useful for exposing typed interfaces rather than plain messaging, especially when multiple message types are expected at an event-bus destination. Testing is also an important concept, and we’ll look at what is different in testing asynchronous Vert.x code compared to traditional testing.
In this chapter we will revisit an earlier example, refactor it into an event-bus service, and test it.
In chapter 3 we used heat sensors as an example. We had a SensorData verticle that kept the last observed values for each sensor and compute their average using request/reply communication on the event bus. The following listing shows the code we used to compute the temperature average.
private void average(Message<JsonObject> message) { #1
double avg = lastValues.values().stream()
.collect(Collectors.averagingDouble(Double::doubleValue));
JsonObject json = new JsonObject().put("average", avg);
message.reply(json); #2
}