Enterprise Java Development@TOPIC@

Chapter 105. Context and Dependency Injection (CDI) JSR-299

105.1. History
105.2. Injection Concept
105.3. CDI Activation
105.4. Summary

105.1. History

105.2. Injection Concept

Figure 105.1. Beans

@Named

public class JPASchedulerDAOImpl extends JPADAOBase<Task> implements SchedulerDAO {

@Stateless

public class CookEJB extends SchedulerBase implements CookLocal {

  • Beans can be simple POJOs, EJBs, Servlets, etc.

  • CDI Beans generalize behavior provided by larger frameworks

Figure 105.2. Injection

@Inject

protected Scheduler cook; 

  • Type-safe, Java-based container injection

  • Container will match injection point with managed bean of requested type

  • Error if container finds multiple classes satisfying requested type

Figure 105.3. Qualifiers and Qualified Injection

@Inject @Cook

protected Scheduler cook; 
@Stateless

@Cook

public class CookEJB extends SchedulerBase implements CookLocal {

  • @Annotation qualifier specializes injection type to remove ambiguity

Figure 105.4. Qualifier Annotations

package ejava.examples.jndidemo;


import java.lang.annotation.Retention;

import java.lang.annotation.Target;

import static java.lang.annotation.RetentionPolicy.*;

import static java.lang.annotation.ElementType.*;

import javax.inject.Qualifier;


@Qualifier

@Retention(RUNTIME)

@Target({METHOD, FIELD, PARAMETER, TYPE})

public @interface Cook {

}

  • java.lang.annoation

    @Retention

    how long the class is retained (default=CLASS)

    RententionPolict

    • CLASS - annotation recorded in class file but not available at runtime

    • RUNTIME - annotation recorded in class and available at runtime

    • SOURCE - annotation discarded by compiler

    @Target

    kind of Java construct the annotation applies to

    ElementType

    • TYPE

    • FIELD

    • METHOD

    • PARAMETER

    • (more)

  • javax.inject (JSR-330)

    @Inject

    an injection target

    @Named

    string qualifier (for JSPs, etc. to reference bean using text)

    @Qualifier

    identifies qualifier annotations

  • javax.enterprise.inject (JSR-299)

    @Produces

    an injection source

    @Any

    no qualifiers

    Instance<Bean>

    runtime source of type Bean

105.3. CDI Activation

Activated when beans.xml is located in appropriate location

Figure 105.5. beans.xml


<?xml version="1.0" encoding="UTF-8"?>

<beans bean-discovery-mode="all" version="1.1"

     xmlns="http://xmlns.jcp.org/xml/ns/javaee"

     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

     xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd">

   <scan>

      <exclude name="info.ejava.examples.ejb.cdisales.dao.UserMgmtDAO"/>

   </scan>

</beans>

  • Can be blank or empty

  • Example shows XML alternative to using @Veto - which makes a bean unavailable for injection

105.4. Summary