CDI vs Guice: What are the differences?

Introduction

In this Markdown code, we will discuss the key differences between CDI (Contexts and Dependency Injection) and Guice, two popular frameworks used for dependency injection in Java.

1. Scopes: CDI provides a more extensive set of scopes than Guice. It includes the standard scopes like @RequestScoped, @SessionScoped, and @ApplicationScoped, as well as additional custom scopes. Guice, on the other hand, only includes the @Singleton scope by default.

2. Configuration: CDI uses a declarative approach to configuration, where dependencies and their relationships are defined using annotations in the code itself. Guice, on the other hand, uses a more explicit and programmatic approach, where configuration is done via Java code in separate modules.

3. Interceptors and Decorators: CDI provides built-in support for interceptors, allowing method invocations to be intercepted and modified by additional logic. It also supports decorators, which allow the customization of existing instances with additional behavior. Guice, on the other hand, does not have built-in support for interceptors and decorators. Instead, they need to be implemented manually.

4. Event System: CDI provides an event system, allowing objects to publish events and other objects to observe and handle these events. Guice, on the other hand, does not have a built-in event system.

5. Type-Safe Injection: CDI supports type-safe injection using its built-in type-safe resolution mechanism. This allows for compile-time checking and validation of the injection points. Guice, on the other hand, does not provide this type-safe resolution mechanism and relies on runtime reflection for injection.

6. Integration with Java EE: CDI is a part of the Java EE (Enterprise Edition) specification and integrates seamlessly with other Java EE technologies like Servlets, EJBs, and JPA. Guice, on the other hand, is not a part of the Java EE specification but can still be used in Java EE projects with some additional configuration.

In Summary, CDI offers a broader range of scopes, supports interceptors and decorators, comes with an event system, provides type-safe injection, and integrates well with Java EE technologies. On the other hand, Guice uses a more explicit configuration approach, does not have built-in support for interceptors and decorators or an event system, and is not a part of the Java EE specification.