CDI — Dependency Injection in Java EE

CDI (Contexts and Dependency Injection) is the standard DI framework in Java EE. Since version 6 it has been part of the specification and finally delivers what Spring has had for years — type-safe dependency injection with annotations.

CDI basics¶

@Inject instead of new. The container manages object lifecycle and resolves dependencies automatically. No XML configuration — CDI uses annotations and convention. Every class with a beans.xml in META-INF/WEB-INF is a CDI bean.

Scopes¶

@RequestScoped — new object per HTTP request. @SessionScoped — per HTTP session. @ApplicationScoped — singleton. @ConversationScoped — explicitly managed scope across multiple requests. @Dependent — default, new object at every injection point. Choosing the right scope is critical for correct behavior and performance.

Producers¶

@Produces methods create objects that the CDI container cannot produce automatically (EntityManager, configuration values, external resources). An alternative to the factory pattern — cleaner and more declarative.

Interceptors and Decorators¶

Interceptors for cross-cutting concerns: @Interceptor with @AroundInvoke for logging, security, caching. The @Transactional interceptor replaces EJB transactions. Decorators for extending business logic without modifying the original.

CDI vs. Spring DI¶

CDI: standard, part of Java EE, type-safe qualifiers. Spring: older, larger ecosystem, works without an app server. For Java EE projects: CDI. For Spring projects: Spring DI. Don’t mix both in the same application.

Conclusion¶

CDI is a mature DI framework. For Java EE projects it is the preferred choice — standard, type-safe and with excellent integration with EJB and JPA. Spring DI remains the better choice outside the Java EE container.