Contexts and Dependency Injection (CDI) in Java EE

1. Introduction

Contexts and Dependency Injection (CDI) is a powerful set of services that allows Java EE developers to manage the lifecycle of Java objects in a consistent manner. CDI provides a way to inject dependencies into classes, making it easier to build loosely coupled applications.

2. Key Concepts

3. Setup

To use CDI in your Java EE application, follow these steps:

1. Ensure you have a Java EE compliant server (e.g., WildFly, Payara).
2. Add the required CDI dependencies to your project's build file (Maven/Gradle).
3. Create a beans.xml file in the WEB-INF directory to enable CDI.

 
<beans 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"
       version="1.1">
</beans>
            

4. Usage

CDI allows you to define beans and inject them using the @Inject annotation:

import javax.inject.Inject;

public class UserService {
    public void createUser() {
        System.out.println("User created!");
    }
}

public class UserController {
    @Inject
    UserService userService;

    public void registerUser() {
        userService.createUser();
    }
}
                

In this example, UserService is injected into UserController, enabling it to be used without creating an instance manually.

5. Best Practices

• Limit the number of injected fields to improve readability.
• Use qualifiers to avoid ambiguity when multiple beans of the same type exist.
• Prefer constructor injection over field injection for better testability.

6. FAQ