CDI Bean Life Cycle Management

CDI Beans Life Cycle Management

• In CDI, the container manages the life cycle of beans, resolving dependencies and invoking methods annotated with @PostConstruct before the first business method invocation.
• The @PreDestroy callback notification signals that the instance is being removed by the container.

Scopes and Context

• CDI beans may be stateful and contextual, living in a well-defined scope (e.g., request, session, application, and conversation scopes).

Interception

• Interceptors are used to interpose on business method invocations, similar to aspect-oriented programming (AOP).
• Interceptors can be chained and are called before and/or after method execution.
• They separate technical concerns from business logic.

Loose Coupling and Strong Typing

• Interceptors separate technical concerns from business logic.
• CDI uses strongly typed annotations to wire beans together.

Deployment Descriptor

• The deployment descriptor is called beans.xml and is mandatory.
• It can be used to configure functionalities (interceptors, decorators, alternatives, etc.).

Understanding Beans

• Beans are CDI objects built on the Managed Bean model.
• They have an improved life cycle for stateful objects, are bound to well-defined contexts, and bring a typesafe approach to dependency injection, interception, and decoration.

Dependency Injection

• Dependency Injection (DI) is a design pattern that decouples dependent components.
• It is part of inversion of control, where the container injects dependent objects.

Life Cycle of a POJO

• The life cycle of a POJO is simple: create an instance using the new keyword and wait for the Garbage Collector to free memory.

CDI Bean Life Cycle

• To run a CDI Bean inside a container, you can't use the new keyword; instead, you need to inject the bean and the container manages its life cycle.
• The container creates the instance, gets rid of it, and gives a handle after constructing and before destroying it.

CDI Specifications Overview

• The aim of CDI was to fill gaps in the platform, knit together the web tier and transactional tier, make dependency injection first-class, and add extensions easily.
• CDI 2.0 added support for Java SE, API to boot CDI in Java SE, observers (events) ordering, asynchronous events, configurators, possibility to configure or veto observer methods, built-in annotation literals, and alignment with Java 8 features.

Writing a CDI Bean

• A CDI Bean can be any class containing business logic, called directly via injection or invoked via EL from a JSF page.
• A bean is a POJO that doesn't inherit or extend from anything, can inject references to other beans, has its life cycle managed by the container, and can get its method invocation intercepted.