What is CDI?

CDI (Contexts and Dependency Injection) is a powerful Java EE (Enterprise Edition) standard that provides a set of technologies for managing objects and their dependencies in a Java application. It allows developers to write loosely coupled and highly maintainable code by promoting the use of dependency injection and supporting different scopes and contexts.

CDI is built on top of other Java EE technologies like JavaBeans, Java Annotations, and Java Persistence API (JPA). It provides a standardized approach for managing object lifecycles, performing dependency injection, and enabling communication between different application components.

Key Features of CDI

1. Dependency Injection (DI): CDI simplifies the process of injecting dependencies into classes by managing the creation and lifecycle of objects. It allows you to specify dependencies using annotations, removing the need for manual object instantiation and making your code more modular and testable.

2. Contexts: CDI defines several contexts that allow you to manage the lifecycle and visibility of objects. The built-in contexts include @ApplicationScoped, @SessionScoped, @RequestScoped, and @Dependent. These contexts define the lifespan of an object based on their associated scopes.

3. Events: CDI provides an event-driven programming model where components can publish and observe events. This enables loose coupling between components and allows them to communicate without direct dependencies.

4. Interceptors: CDI supports interceptors that can be used to add cross-cutting concerns such as logging, security, and performance monitoring to your application. Interceptors can intercept method invocations on managed beans and apply additional behaviors before and after the execution.

5. Qualifiers: CDI introduces the concept of qualifiers, which allows you to differentiate between beans of the same type. Qualifiers can be used to select the appropriate bean for injection when multiple beans of the same type exist in the application.

Getting Started with CDI

To use CDI in a Java application, you need to include the necessary dependencies in your project’s build configuration. CDI is part of the Java EE standard, so it is already included in most Java EE application servers.

Once you have the dependencies set up, you can start using CDI by annotating your classes with CDI-specific annotations like @Inject, @Named, and @ApplicationScoped. These annotations allow CDI to manage the lifecycle and injection of objects.

Here is an example of using CDI to inject a dependency into a class:

import javax.inject.Inject;

@ApplicationScoped
public class UserService {
    @Inject
    private UserRepository userRepository;
    
    // ...
}

In the above example, UserService is an application-scoped CDI bean, and it injects a UserRepository dependency using the @Inject annotation.

CDI offers much more functionality than what’s covered in this brief introduction. If you want to dive deeper into CDI and explore its advanced features, consider referring to the official documentation and tutorials.

#Java #CDI