Contexts and Dependency Injection (CDI): Eager Extensions

CDI does not provide eager extensions out of the box. Even though there is @ApplicationScoped, which is intended to work in a similar way to eager instantiation, it does not behave in the specified fashion. 

I am going to describe how to use CDI extensions to get eagerly instantiated beans following the CDI lifecycle — inside the container. I have used this in Wildfly 8.0. 

The Process

Step 1: First, write the @Eager annotation.

 package me.sumithpuri.test.cdi.annotation;

 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 import javax.inject.Qualifier;

 @Qualifier
 @Retention(RetentionPolicy.RUNTIME)
 @Target({
     ElementType.FIELD,
     ElementType.TYPE,
     ElementType.METHOD,
     ElementType.PARAMETER
 })
 public @interface Eager {}

Step 2: Next, develop the Eager Extension to parse the annotations.

 package me.sumithpuri.test.cdi.extension;

 import java.util.ArrayList;
 import java.util.List;
 import javax.enterprise.context.ApplicationScoped;
 import javax.enterprise.event.Observes;
 import javax.enterprise.inject.spi.AfterDeploymentValidation;
 import javax.enterprise.inject.spi.Bean;
 import javax.enterprise.inject.spi.BeanManager;
 import javax.enterprise.inject.spi.Extension;
 import javax.enterprise.inject.spi.ProcessBean;
 import me.sumithpuri.test.cdi.annotation.Eager;

 public class EagerExtension implements Extension {

     private List < Bean << ? >> eagerBeansList = new ArrayList < Bean << ? >> ();

     public < T > void collect(@Observes ProcessBean < T > event) {
         if (event.getAnnotated().isAnnotationPresent(Eager.class) &&
             event.getAnnotated().isAnnotationPresent(ApplicationScoped.class)) {
             System.out.println("debug: found an eager annotation");
             eagerBeansList.add(event.getBean());
         }
     }

     public void load(@Observes AfterDeploymentValidation event, BeanManager beanManager) {
         for (Bean << ? > bean : eagerBeansList) {
             System.out.println("debug: eager instantiation will be performed - " + bean.getBeanClass());
             // note: toString() is important to instantiate the bean  
             beanManager.getReference(bean, bean.getBeanClass(), beanManager.createCreationalContext(bean)).toString();
         }
     }
 }

Step 3: Next, configure the extension using this single line of code, placed inside META-INF/services/javax.enterprise.inject.spi.Extension

 me.sumithpuri.test.cdi.extension.EagerExtension  

Step 4: Develop the other parts of the application.

You can refer to the attached code to develop the other parts of the application to test CDI (@Eager). You may download the code from here. Also, note that even though all lifecycle methods are performed such @PostConstruct, @PreDestroy, etc. — no @Inject is being performed. My assumption is that we have to write another extension to perform this. My request to the CDI creators to provide an @Eager out of the box, so that it can help to develop (and sometimes help in testing) applications where dependency injection can be performed outside of servlets, web sServices, etc.