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Vert.x defines itself as "a toolkit for building reactive applications on the JVM".
- Sounds cool and trendy.
- Weld, on the other hand, comes from the Java EE world, based on standards and traditional concepts.
- But wait, what if we try to combine the two worlds to get the best of them?
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Vert.x makes use of a light-weight distributed messaging system to allow application components to communicate in a loosely coupled way.
- This should sound familiar to all CDI users where beans may produce and consume events as well.
- Weld team developed a working prototype of Weld/Vert.x integration that allows to automatically register certain observer methods as Vert.x message consumers.
- A simple echo message consumer could look like this:
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import org.jboss.weld.vertx.VertxConsumer;
import org.jboss.weld.vertx.VertxEvent;
class Foo {
public void echoConsumer(@Observes @VertxConsumer("test.echo.address") VertxEvent event) {
event.setReply(event.getMessageBody());
}
}
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Since we’re working with a regular observer method, additional parameters may be declared (next to the event parameter).
- These parameters are injection points. So it’s easy to declare a message consumer dependencies:
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public void consumerWithDependencies(@Observes @VertxConsumer("test.dependencies.address") VertxEvent event, CoolService coolService, StatsService statsService) {
coolService.process(event.getMessageBody());
statsService.log(event);
}
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- Note
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- If you inject a dependent bean, it will be destroyed when the invocation completes.
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Last but not least - an observer may also send/publish messages using the Vert.x event bus:
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public void consumerStrikesBack(@Observes @VertxConsumer("test.publish.address") VertxEvent event) {
event.messageTo("test.huhu.address").publish("huhu");
}
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And how does it work under the hood?
- First of all, it’s necessary to deploy org.jboss.weld.vertx.WeldVerticle.
- This Verticle starts Weld SE container and automatically registers org.jboss.weld.vertx.VertxExtension to process all observer methods and detect observers which should become message consumers.
- Then a special handler is registered for each address to bridge the event bus to the CDI world.
- Handlers use Vertx.executeBlocking() since we expect the code to be blocking.
- Later on, whenever a new message is delivered to the handler, Event.fire() is used to notify all relevant observers.
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The prototype is surely missing some features. Nevertheless, it shows the CDI programming model might be applicable to the "reactive" world even if not a first class citizen.
- Moreover, the prototype demonstrates the flexibility of the CDI extension mechanism.
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If you want to try it out, you’ll have to clone the https://github.com/weld/weld-vertx repository and build it from source (i.e. run mvn clean install).
- And if you find it useful feel free to add comments to this blog post. Any feedback is appreciated!
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