Jakarta CDI - Intermediate Lab 1

In this lab, we will create an object and destroy objects using the Produces and Dispose annotations, respectively.

1. Create the NumberProducer class

Steps

1. Open the 01-jakarta-ee project and navigate to the src/main/java
2. Create a package named producer in the expert.os.labs.persistence.cid package
3. Create a class called NumberProducer in the expert.os.labs.persistence.cid.producer package
4. Annotate it with the @ApplicationScoped from the jakarta.enterprise.context package
5. Add a producer method, annotating it with @Produces from the jakarta.enterprise.inject package and generate a random BigDecimal value within the range [1, 100] using the ThreadLocalRandom and return it
6. Add a disposer method named destroy() to remove the value from the class where it has a value parameter annotated with @Disposes from the jakarta.enterprise.inject package

Solution

Click to see...

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.inject.Disposes;
import jakarta.enterprise.inject.Produces;

import java.math.BigDecimal;
import java.util.concurrent.ThreadLocalRandom;

@ApplicationScoped
public class NumberProducer {

    @Produces
    public BigDecimal producer() {
        ThreadLocalRandom random = ThreadLocalRandom.current();
        double nextDouble = random.nextInt(1, 100);
        return new BigDecimal(nextDouble);
    }

    public void destroy(@Disposes BigDecimal value) {
        System.out.println("We don't need this number anymore: " + value);
    }
}

2. Create the app class

Steps

1. Create a class called AppNumber 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 BigDecimal through the container instance

5. Printout the value
6. Run the main() method

Expected results

• The following output

  Value = <number>
  We don't need this number anymore: <number>
  

  Note

  The destroy() method is used as a disposer method for BigDecimal instances. It takes a parameter of type BigDecimal annotated with @Disposes. When an instance of BigDecimal is no longer needed, the CDI container will automatically call this method to perform cleanup or logging. In this case, it prints a message indicating that the number is no longer needed.

  In summary, this code defines an application-scoped CDI bean (NumberProducer) that produces random BigDecimal values using a producer method. It also includes a disposer method to handle the cleanup of BigDecimal instances when they are no longer needed within the CDI context.

Solution

Click to see...

import jakarta.enterprise.inject.se.SeContainer;
import jakarta.enterprise.inject.se.SeContainerInitializer;

import java.math.BigDecimal;

public class AppNumber {

    public static void main(String[] args) {
        try (SeContainer container = SeContainerInitializer.newInstance().initialize()) {
            BigDecimal value = container.select(BigDecimal.class).get();
            System.out.println("Value = " + value);
        }
    }
}