Jakarta CDI - Intermediate Lab 3

In this lab, we will explore more about the CDI events.

1. Create the LoggerProducer class

Steps

1. Create a new package called news in the expert.os.labs.persistence.cid package
2. Create the class News in the expert.os.labs.persistence.cid.news
3. Implements the Supplier<String> interface and it's method get()
4. Add a private String field named name
5. Create a constructor to associate its name
6. Add a factory method of() that will create a new instance of News
7. Make the get() method return the value of the name attribute

Solution

Click to see...

public final class News implements Supplier<String> {

    private String name;

    public News(String name) {
        this.name = name;
    }

    public static News of(String news) {
        return new News(news);
    }

    @Override
    public String get() {
        return name;
    }
}

2. Create the MAgazine class

Steps

1. Create a class called Magazine in the expert.os.labs.persistence.cid.news package
2. Implements the Consumer<News> and the method accept()
   • the Consumer class is from the java.util.function package
3. Define a private attribute Logger from the java.util.logging package
4. Add the @Observes annotation to the News attribute in the accept() method, where it's from the jakarta.enterprise.event package
5. Log the News in the accept() method

Solution

Click to see...

import jakarta.enterprise.event.Observes;

import java.util.function.Consumer;
import java.util.logging.Logger;

public class Magazine implements Consumer<News> {

    private static final Logger LOGGER = Logger.getLogger(Magazine.class.getName());

    @Override
    public void accept(@Observes News news) {
        LOGGER.info("We got the news, we'll publish it on a magazine: " + news.get());
    }
}

3. Create the NewsPaper class

Steps

1. Create a class called NewsPapper in the expert.os.labs.persistence.cid.news package
2. Annotate it with @ApplicationScoped from the jakarta.enterprise.context package
3. Implements the Consumer<News> and the method accept()
   • the Consumer class is from the java.util.function package
4. Define a private attribute Logger from the java.util.logging package
5. Add the @Observes annotation to the News attribute in the accept() method, where it's from the jakarta.enterprise.event package
6. Log the News in the accept() method

Solution

Click to see...

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.event.Observes;

import java.util.function.Consumer;
import java.util.logging.Logger;

@ApplicationScoped
public class NewsPaper implements Consumer<News> {

    private static final Logger LOGGER = Logger.getLogger(NewsPaper.class.getName());

    @Override
    public void accept(@Observes News news) {
        LOGGER.info("We got the news, we'll publish it on a newspaper: " + news.get());
    }
}

4. Create the SocialMedia class

Steps

1. Create a class called SocialMedia in the expert.os.labs.persistence.cid.news package
2. Annotate it with @ApplicationScoped from the jakarta.enterprise.context package
3. Implements the Consumer<News> and the method accept()
   • the Consumer class is from the java.util.function package
4. Define a private attribute Logger from the java.util.logging package
5. Add the @Observes annotation to the News attribute in the accept() method, where it's from the jakarta.enterprise.event package
6. Log the News in the accept() method

Solution

Click to see...

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.event.Observes;

import java.util.function.Consumer;
import java.util.logging.Logger;

@ApplicationScoped
public class SocialMedia implements Consumer<News> {

    private static final Logger LOGGER = Logger.getLogger(SocialMedia.class.getName());

    @Override
    public void accept(@Observes News news) {
        LOGGER.info("We got the news, we'll publish it on Social Media: " + news.get());
    }
}

5. Create the Journalist class

Steps

1. Create a class called Journalist in the expert.os.labs.persistence.cid.news package
2. Annotate it with @ApplicationScoped from the jakarta.enterprise.context package
3. Create a private Event<News> field and annotate it with @Inject from jakarta.inject package
   • The Event is from the jakarta.enterprise.event package
4. Create a method named receiveNews with a News parameter which will fire and event (this.event.fire())

Solution

Click to see...

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.event.Event;
import jakarta.inject.Inject;

@ApplicationScoped
public class Journalist {

    @Inject
    private Event<News> event;

    public void receiveNews(News news) {
        this.event.fire(news);
    }
}

6. Create the app class

Steps

1. Create a class called AppJournalist in the expert.os.labs.persistence.cid package

2. Add a main method

   public static void main(String[] args) {
   }
   

3. Set up a try-with-resources block, inside the main method, to manage the Jakarta EE SeContainer that is responsible for dependency injection and managing resources

   try (SeContainer container = SeContainerInitializer.newInstance().initialize()) {     
   }
   

4. Obtain the value of the Journalist through the container instance

5. Printout the news using the method receiveNews from the Journalist using the News.of()

Expected results

• The following output

  INFO: We got the news, we'll publish it on Social Media: <the news you defined>
  

Solution

Click to see...

import expert.os.labs.persistence.cdi.news.Journalist;
import expert.os.labs.persistence.cdi.news.News;
import jakarta.enterprise.inject.se.SeContainer;
import jakarta.enterprise.inject.se.SeContainerInitializer;

public class AppJournalist {

    public static void main(String[] args) {
        try (SeContainer container = SeContainerInitializer.newInstance().initialize()) {
            Journalist journalist = container.select(Journalist.class).get();
            journalist.receiveNews(News.of("Java 21 has arrived!!"));
        }
    }
}