Jakarta CDI - Intermediate Lab 2

In this lab, we will create an object taking information from who needs this information using the InjectionPoint. Thus, we will create a Logger producer.

1. Create the LoggerProducer class

Steps

1. Create a class called LoggerProducer in the expert.os.labs.persistence.cid.producer package
2. Create a constant to log results using the Logger from the java.util.logging package
3. Annotate it with the @ApplicationScoped from the jakarta.enterprise.context package
4. Add a producer method, annotating it with @Produces from the jakarta.enterprise.inject where:
   • it has a parameter using the InjectionPoint class from jakarta.enterprise.inject.spi package
   • get the class name using the Injection point, associating it with a variable
   • log the class name using the logger

Solution

Click to see...

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.inject.Produces;
import jakarta.enterprise.inject.spi.InjectionPoint;

import java.util.logging.Logger;

@ApplicationScoped
public class LoggerProducer {

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

    @Produces
    Logger getLog(InjectionPoint injectionPoint) {
        String declaringClass = injectionPoint.getMember().getDeclaringClass().getName();
        LOGGER.info("Creating instance log to " + declaringClass);

        return Logger.getLogger(declaringClass);
    }
}

Note

The getLog() method is annotated with @Produces, indicating that it is a CDI producer method. This method produces java.util.logging.Logger instances. It takes an InjectionPoint as a parameter, which provides information about the injection point. It retrieves the declaring class name from the injection point and creates a Logger instance for that class name. It also logs a message indicating the creation of the logger.

2. Define a class that uses the produced logger

Steps

1. Create a class called NumberLogger in the expert.os.labs.persistence.cid package
2. Define a private attribute Logger from the java.util.logging package
3. Add a default constructor
4. Add a constructor that receives the Logger as a parameter and annotate it using the @Inject class from the jakarta.inject package
5. Add a log method to log a BigDecimal value

Solution

Click to see...

import jakarta.inject.Inject;

import java.math.BigDecimal;
import java.util.logging.Logger;

public class NumberLogger {

    private Logger logger;

    NumberLogger() {
    }

    @Inject
    public NumberLogger(Logger logger) {
        this.logger = logger;
    }

    public void log(BigDecimal value) {
        this.logger.info("The BigDecimal value is " + value);
    }

}

3. Create the app class

Steps

1. Create a class called AppNumberLog 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. Obtain the value of the NumberLogger through the container instance
6. Printout the value of the NumberLogger
7. Run the main() method

Expected results

• The following output

  expert.os.labs.persistence.cdi.producer.LoggerProducer getLog
  INFO: Creating instance log to expert.os.labs.persistence.cdi.NumberLogger
  expert.os.labs.persistence.cdi.NumberLogger log
  INFO: The BigDecimal value is 11
  We don't need this number anymore: 11
  

Solution

Click to see...

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

import java.math.BigDecimal;

public class AppNumberLog {

    public static void main(String[] args) {
        try (SeContainer container = SeContainerInitializer.newInstance().initialize()) {
            BigDecimal value = container.select(BigDecimal.class).get();

            NumberLogger logger = container.select(NumberLogger.class).get();
            logger.log(value);
        }
    }
}