Home » Java » Enterprise Java » Java EE CDI Qualifiers: Quick Peek

About Abhishek Gupta

Java EE CDI Qualifiers: Quick Peek

Qualifiers are the mainstay of type safety and loose coupling in Contexts and Dependency Injection (CDI). Why? Without CDI, we would be injecting Java EE components in a manner similar to below

Note:This will actually not compile and is just a hypothetical code snippet

 
 
 
 
 

Example 1

cdi1

 

Example 2

cdi2

What’s wrong with the above implementations?

  • Not type safe – Uses a String to specify the fully qualified name of an implementation class (see Example 1)
  • Tightly couples the BasicCustomerPortal class to the BasicService class (see Example 2)

This is exactly why CDI does not do Injection this way !

Qualifiers help promote

  • Loose Coupling – An explicit class is not introduced within another. Detaches implementations from each other
  • Strong Typing (type safety) – No String literals to define injection properties/metadata

 Qualifiers also serve as

  • Binding components between beans and Decorators
  • Event selectors for Observers (event consumers)

 

How to use Qualifiers? 

CDI Qualifiers Simplified

cdi-qualifiers-simplified

 

 Simplified steps

  • Create a Qualifier
  • Apply Qualifiers to different implementation classes
  • Use the Qualifiers along with @Inject to inject the instance of the appropriate implementation within a class

This was not a detailed or in-depth post about CDI Qualifiers. It’s more of a quick reference.

More on CDI

Thanks for reading!

Reference: Java EE CDI Qualifiers: Quick Peek from our JCG partner Abhishek Gupta at the Object Oriented.. blog.

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

1. JPA Mini Book

2. JVM Troubleshooting Guide

3. JUnit Tutorial for Unit Testing

4. Java Annotations Tutorial

5. Java Interview Questions

6. Spring Interview Questions

7. Android UI Design

and many more ....

 

Leave a Reply

Your email address will not be published. Required fields are marked *

*


nine + 7 =

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

Do you want to know how to develop your skillset and become a ...

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!
Get ready to Rock!
To download the books, please verify your email address by following the instructions found on the email we just sent you.

THANK YOU!

Close