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How to handle exception using onException() in Spring Boot Camel

Spring boot Apache Camel-Java DSL app reads messages from Kafka topic.
#Component
public class KafkaTopicService extends RouteBilder {
public void configure(){
from("kafka:myTopic?brokers=localhost:9092")
.log("Message received from Kafka: ${body}")}
}
If I stop Kafka I get org.apache.kafka.common.errors.DisconnectException
I looked into onException(...class).handled(true) but Im not sure how to implement handling of the exception in my code. Can someone give me few implementation examples? What options are available? For example logging the message or reattempting to read message?
Documentation also mentions Quarkus. Do I need Quarkus to use onException()?

You can do something like (have not tried running it so please take care of any typos)
#Component
public class KafkaTopicService extends RouteBilder {
public void configure(){
onException(org.apache.kafka.common.errors.DisconnectException.class)
.log("Error connecting kafka");
from("kafka:myTopic?brokers=localhost:9092&bridgeErrorHandler=true")
.log("Message received from Kafka: ${body}")}
}
Please note that I have added bridgeErrorHandler=true. Normally exception handling happens after from. In most of the case using bridgeErrorHandler we can use onException function for those.
Also note that I have defined onException outside your route, so the exception handling logic which you add would be global and applicable to all routes wherever you encounter DisconnectException

Service is stuck when using #CacheResult

I'm trying to cache some expensive db operations in my quarkus project.
But when I'm adding a #CacheResult annotation, the program is getting stuck before the method execution.
Class is annotated as #ApplicationScoped.
There's also #Transactional annotation.
Method looks like:
#Override
#CacheResult(cacheName = "some-chain")
public List<UUID> getChain(#CacheKey UUID someId){
// Call to the Spring Data repository and some additional logic
}
Thread dump shows that everything is in Waiting or Runnable state.
It looks like a deadlock. Dear community, please help me to solve it )
PS. When I remove request to DB from this method, everything works as expected.

Vert.x Unit Test a Verticle that does not implement the start method with future

I'm new to Vert.x and just stumbled about a problem.
I've the following Verticle:
public class HelloVerticle extends AbstractVerticle {
#Override
public void start() throws Exception {
String greetingName = config().getString("greetingName", "Welt");
String greetingNameEnv = System.getenv("GREETING_NAME");
String greetingNameProp = System.getProperty("greetingName");
Router router = Router.router(vertx);
router.get("/hska").handler(routingContext -> {
routingContext.response().end(String.format("Hallo %s!", greetingName));
});
router.get().handler(routingContext -> {
routingContext.response().end("Hallo Welt");
});
vertx
.createHttpServer()
.requestHandler(router::accept)
.listen(8080);
}
}
I want to unit test this verticle but i dont know how to wait for the verticle to be deployed.
#Before
public void setup(TestContext context) throws InterruptedException {
vertx = Vertx.vertx();
JsonObject config = new JsonObject().put("greetingName", "Unit Test");
vertx.deployVerticle(HelloVerticle.class.getName(), new DeploymentOptions().setConfig(config));
}
when i setup my test like this i have to add a Thread.sleep after the deploy call, to make the tests be executed after some time of watiting for the verticle.
I heared about Awaitability and that it should be possible to wait for the verticle to be deployed with this library. But I didn't find any examples of how to use Awaitability with vertx-unit and the deployVerticle method.
Could anyone bring some light into this?
Or do i really have to hardcode a sleep timer after calling the deployVerticle-Method in my tests?
Have a look into the comments of the accepted answer

First of all you need to implement start(Future future) instead of just start(). Then you need to add a callback handler (Handler<AsyncResult<HttpServer>> listenHandler) to the listen(...) call — which then resolves the Future you got via start(Future future).
Vert.x is highly asynchronous — and so is the start of an Vert.x HTTP server. In your case, the Verticle would be fully functional when the HTTP server is successfully started. Therefore, you need implement the stuff I mentioned above.
Second you need to tell the TestContext that the asynchronous deployment of your Verticle is done. This can be done via another callback handler (Handler<AsyncResult<String>> completionHandler). Here is blog post shows how to do that.
The deployment of a Verticle is always asynchronous even if you implemented the plain start() method. So you should always use a completionHandler if you want to be sure that your Verticle was successfully deployed before test.
So, no you don't need to and you definitely shouldn't hardcode a sleep timer in any of your Vert.x applications. Mind The Golden Rule - Don’t Block the Event Loop.
Edit:
If the initialisation of your Verticle is synchronous you should overwrite the plain start() method — like it's mentioned in the docs:
If your verticle does a simple, synchronous start-up then override this method and put your start-up code in there.
If the initialisation of your Verticle is asynchronous (e.g. deploying a Vert.x HTTP server) you should overwrite start(Future future) and complete the Future when your asynchronous initialisation is finished.

Example of Spring Boot, RabbitMQ Listener responding with nack

I'm having trouble finding an example of a RabbitMQ listener responding with a nack in Spring Boot. Anyone got any resources?? I'm a complete noob, I've read through the docs a couple times but can't find anything I can easily grok.

For future viewers, I haven't fully tested this yet but I discovered that a method with the annotation #RabbitHandler (within a class annotated with #RabbitListener) can accept a channel and then use that channel to respond with a nack.
#RabbitHandler
public void process(..., Channel channel) {
channel.basicNack(...)
}
http://docs.spring.io/spring-integration/reference/html/amqp.html

java ee background service

You'll have to excuse me if I'm describing this incorrectly, but essentially I'm trying to get a service-like class to be instantiated just once at server start and to sort of "exist" in the background until it is killed off at server stop. At least from what I can tell, this is not exactly the same as a typical servlet (though I may be wrong about this). What's even more important is that I need to also be able to access this service/object later down the line.
As an example, in another project I've worked on, we used the Spring Framework to accomplish something similar. Essentially, we used the configuration XML file along with the built-in annotations to let Spring know to instantiate instances of some of our services. Later down the line, we used the annotation #Autowired to sort of "grab" the object reference of this pre-instantiated service/object.
So, though it may seem against some of the major concepts of Java itself, I'm just trying to figure out how to reinvent this wheel here. I guess sometimes I feel like these big app frameworks do too much "black-box magic" behind the scenes that I'd really like to be able to fine-tune.
Thanks for any help and/or suggestions!
Oh and I'm trying to run this all from JBoss 6

Here's one way to do it. Add a servlet context listener to your web.xml, e.g.:
<listener>
<listener-class>com.example.BackgroundServletContextListener</listener-class>
</listener>
Then create that class to manage your background service. In this example I use a single-threaded ScheduledExecutorService to schedule it to run every 5 minutes:
public class BackgroundServletContextListener implements ServletContextListener {
private ScheduledExecutorService executor;
private BackgroundService service;
public void contextInitialized(ServletContextEvent sce) {
service = new BackgroundService();
// setup single thread to run background service every 5 minutes
executor = Executors.newSingleThreadScheduledExecutor();
executor.scheduleAtFixedRate(service, 0, 5, TimeUnit.MINUTES);
// make the background service available to the servlet context
sce.getServletContext().setAttribute("service", service);
}
public void contextDestroyed(ServletContextEvent sce) {
executor.shutdown();
}
}
public class BackgroundService implements Runnable {
public void run() {
// do your background processing here
}
}
If you need to access the BackgroundService from web requests, you can access it through the ServletContext. E.g.:
ServletContext context = request.getSession().getServletContext();
BackgroundService service = (BackgroundService) context.getAttribute("service");

Have you considered using an EJB 3.1 Session bean? These can be deployed in a war file, and can be annotated with #Singleton and #Startup.
A number of annotations available with EJB 3.1 are designed to bring Spring goodies into the Java EE framework. It may be the re-invention you're considering has been done for you.

If you must roll your own, you can create a servlet and configure it start up when the application does using load-on-startup. I built a system like that a few years ago. We then used the new(ish) java.util.concurrent stuff like ExecutorService to have it process work from other servlets.
More information about what you're trying to do, and why the existing ways of doing things is insufficient, would be helpful.

You can use messaging for that. Just send message to the queue, and let the message listener do the processing asynchronously in the background.
You can use JMS for the implementation, and ActiveMQ for the message broker.
Spring has JMSTemplate, JMSGateWaySupport API to make JMS Implementation simple
http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/jms.html