1. Bring your favorite Kafka to Java EE with CDI
Ivan St. Ivanov

2. Who am I?
@ivan_stefanov

3. Agenda
Kafka
Kafka portable

4. Showcase app
User service
Forum service
Kafka
User DB
Forum DB

6. CDI primer @ApplicationScoped public class UserModificationObserver {
     private KafkaProducer<String, String> kafkaProducer;
     public void userModified(User modifiedUser) {
        String record = modifiedUser.toJson().toString();
        kafkaProducer.send(new ProducerRecord<>("user",                            record));
    } }

7. CDI primer @ApplicationScoped public class UserModificationObserver {
   
     private KafkaProducer<String, String> kafkaProducer;
     public void userModified(User modifiedUser) {
        String record = modifiedUser.toJson().toString();
        kafkaProducer.send(new ProducerRecord<>("user",                            record));
    } }

8. CDI primer @ApplicationScoped public class UserModificationObserver {
   
    = "mykafkahost:9090")
     private KafkaProducer<String, String> kafkaProducer;
     public void userModified(User modifiedUser) {
        String record = modifiedUser.toJson().toString();
        kafkaProducer.send(new ProducerRecord<>("user",                            record));
    } }

9. CDI primer public @interface KafkaProducerConfig {
    
    Class keyType() default String.class;
   
    Class valueType() default String.class;
    String bootstrapServers() default "localhost:9092"; }

10. CDI primer @ApplicationScoped public class KafkaProducerFactory {
    public <K,V> KafkaProducer<K, V> createProducer(            InjectionPoint injectionPoint) {
        KafkaProducerConfig annotation = injectionPoint             .getAnnotated()             .getAnnotation(KafkaProducerConfig.class);
        Properties producerProperties = new Properties();
        producerProperties.setProperty(           "bootstrap.servers", annotation.bootstrapServers());
        // Set other props
        return new KafkaProducer<>(producerProperties);
    } }

11. CDI primer @ApplicationScoped public class UserModificationObserver {
   
    = "mykafkahost:9090")
     private KafkaProducer<String, String> kafkaProducer;
     public void User modifiedUser) {
        String record = modifiedUser.toJson().toString();
        kafkaProducer.send(new ProducerRecord<>("user",                            record));
    } }

12. CDI primer public class KafkaUpdatesListener implements Runnable {
= "user")
    private KafkaConsumer<String, String> consumer;
    public void run() {
        while (continuePolling) {
            ConsumerRecords<String, String> records =                consumer.poll(100);
            if (!records.isEmpty()) {
                // Update microservice storage
            }
        }
    }

13. But what if... Leave factories boilerplate to the framework
Leave polling updates to the framework
Do it this way: public class UserModificationKafkaConsumer {
= "user")     public void listenForUsers(                ConsumerRecord<String, String> record) {
        String userJson = record.value();
        // Store the user in DB }

14. CDI extensions CDI magic Hook into the lifecycle
Override default behavior
Portable across containers

15. CDI extension prerequisites
Implement javax.enterprise.inject.spi.Extension
Observe events of interest
Register service provider

16. Process Annotated Types
Before Bean Discovery
Type discovery
Process Annotated Types
After Type Discovery

17. Type discovery Bean discovery Before Bean Discovery
Process Annotated Types
After Type Discovery
Bean discovery
Process Injection Point
Process Injection Target
Process Bean Attributes
Process Bean
Process Producer Method / Field
Process Observer Method
After Bean Discovery
After Deployment Validation

18. Type discovery Bean discovery Running Before Bean Discovery
Process Annotated Types
After Type Discovery
Bean discovery
Process Injection Point
Process Injection Target
Process Bean Attributes
Process Bean
Process Producer Method / Field
Process Observer Method
After Bean Discovery
After Deployment Validation
Running

19. Type discovery Bean discovery Running Before shutdown
Before Bean Discovery
Type discovery
Process Annotated Types
After Type Discovery
Bean discovery
Process Injection Point
Process Injection Target
Process Bean Attributes
Process Bean
Process Producer Method / Field
Process Observer Method
After Bean Discovery
After Deployment Validation
Running
Before shutdown
Before shutdown

20. Kafka CDI extension tasks
Register the factories and listener thread
Create Kafka Consumer for methods
Start polling consumers for changes
methods when change happens

21. Type discovery Bean discovery Running Before shutdown
Before Bean Discovery
Type discovery
Process Annotated Types
public void addKafkaSpecificTypes( BeforeBeanDiscovery bbd,               BeanManager beanManager) {
    bbd.addAnnotatedType(         beanManager.createAnnotatedType(KafkaProducerFactory.class));
    bbd.addAnnotatedType(
        beanManager.createAnnotatedType(KafkaUpdatesListener.class)); }
After Type Discovery
Bean discovery
Process Injection Point
Process Injection Target
Process Bean Attributes
Process Bean
Process Producer Method / Field
Process Observer Method
After Bean Discovery
After Deployment Validation
Running
Before shutdown
Before shutdown

22. Type discovery Bean discovery Running Before shutdown
Before Bean Discovery
Type discovery
Process Annotated Types
After Type Discovery
Bean discovery
Process Injection Point
public void collectConsumerMethods(     ProcessAnnotatedType<?> pat) {
        pat.getAnnotatedType().getMethods().stream()
        .filter(m -> m.isAnnotationPresent(Consumes.class))
        .forEach(m -> handleConsumerMethod(pat.getAnnotatedType(), m)); }
Process Injection Target
Process Bean Attributes
Process Bean
Process Producer Method / Field
Process Observer Method
After Bean Discovery
After Deployment Validation
Running
Before shutdown
Before shutdown

23. Type discovery Bean discovery Running Before shutdown
Before Bean Discovery
Type discovery
Process Annotated Types
After Type Discovery
Bean discovery
Process Injection Point
private void handleConsumerMethod(AnnotatedType<?> clazz,                       AnnotatedMethod<?> am) {
    
    List<AnnotatedParameter<?>> parameters = am.getParameters();
    if (parameters.size() != 1) {
        errors.add(new IllegalArgumentException(
                methods should only have one parameter"));
    } else {
        consumerDescriptors.add(new KafkaConsumerDescriptor(                clazz.getJavaClass(), am,
               am.getAnnotation(Consumes.class).topic()));
    } }
Process Injection Target
Process Bean Attributes
Process Bean
Process Producer Method / Field
Process Observer Method
After Bean Discovery
After Deployment Validation
Running
Before shutdown
Before shutdown

24. Type discovery Bean discovery Running Before shutdown
Before Bean Discovery
Type discovery
Process Annotated Types
After Type Discovery
public void AfterDeploymentValidation adv,                            BeanManager bm) {
    if (!errors.isEmpty()) {
        errors.forEach(adv::addDeploymentProblem);
    } else {
        KafkaUpdatesListener kafkaUpdatesListener = initializeListener(bm);
        startListener(kafkaUpdatesListener, adv);
        this.kafkaUpdatesListener = kafkaUpdatesListener;
    } }
Bean discovery
Process Injection Point
Process Injection Target
Process Bean Attributes
Process Bean
Process Producer Method / Field
Process Observer Method
After Bean Discovery
After Deployment Validation
Running
Before shutdown
Before shutdown

25. Type discovery Bean discovery Running Before shutdown
Before Bean Discovery
Type discovery
Process Annotated Types
After Type Discovery
Bean discovery
Process Injection Point
Process Injection Target
Process Bean Attributes
private KafkaUpdatesListener initializeListener(BeanManager bm) {
    Class<KafkaUpdatesListener> clazz = KafkaUpdatesListener.class;
    KafkaUpdatesListener reference = createBean(bm, clazz);
    consumerDescriptors.forEach(m -> addTopicToListen(m, reference));
    return reference; }
Process Bean
Process Producer Method / Field
Process Observer Method
After Bean Discovery
After Deployment Validation
Running
Before shutdown
Before shutdown

26. Type discovery Bean discovery Running Before shutdown
Before Bean Discovery
Type discovery
Process Annotated Types
After Type Discovery
Bean discovery
Process Injection Point
Process Injection Target
static Object createBean(BeanManager bm, Class<?> clazz) {
    Set<Bean<?>> listenerBeans = bm.getBeans(clazz);
    Bean<?> listenerBean = bm.resolve(listenerBeans);
    CreationalContext<?> creationalContext =                   bm.createCreationalContext(listenerBean);
    return bm.getReference(listenerBean, clazz, creationalContext); }
Process Bean Attributes
Process Bean
Process Producer Method / Field
Process Observer Method
After Bean Discovery
After Deployment Validation
Running
Before shutdown
Before shutdown

27. Type discovery Bean discovery Running Before shutdown
Before Bean Discovery
Type discovery
Process Annotated Types
After Type Discovery
Bean discovery
private void startListener(KafkaUpdatesListener kafkaUpdatesListener) {
    try {
        ExecutorService executorService =          InitialContext.doLookup("java:comp/DefaultManagedExecutorService");      
        executorService.submit(kafkaUpdatesListener);
    } catch (NamingException e) {
        // Handle NamingException
    } }
Process Injection Point
Process Injection Target
Process Bean Attributes
Process Bean
Process Producer Method / Field
Process Observer Method
After Bean Discovery
After Deployment Validation
Running
Before shutdown
Before shutdown

28. Type discovery Bean discovery Running Before shutdown
Before Bean Discovery
Type discovery
Process Annotated Types
After Type Discovery
Bean discovery
Process Injection Point
Process Injection Target
Process Bean Attributes
Process Bean
Process Producer Method / Field
Process Observer Method
public void BeforeShutdown bsh) {
    kafkaUpdatesListener.stopPolling(); }
After Bean Discovery
After Deployment Validation
Running
Before shutdown
Before shutdown

30. Wrap up CDI is powerful Extensions are portable
New features and improvements to add
Create extensions for other libraries
Evangelize

31. Resources The extension https://github.com/bgjug/kafka-cdi-extension
Showcase app
Article by Antoine extensions/
Another Kafka CDI extension