The implementation principle of the CDI API framework in the Java class library

CDI (context and dependency injection) is part of the Java EE (Enterprise Edition), which provides a mechanism for managing dependency relationships between management components.The CDI API framework is a way to implement the CDI specification. It defines standard interfaces and annotations for creating and managing components. The implementation principle of the CDI API framework is as follows: 1. Context management: The CDI framework manages the life cycle of the component through the context manager.The context is a container for components, which can be a thread, a session, a request, etc.The CDI framework defines several different types of contexts, such as application context, session context, and request context.In these contexts, the CDI framework will create and manage component instances. 2. Injecting: The CDI framework uses dependency injection to solve the dependency relationship between components.Dependent injection is a design pattern that allows components to declare other components it needs, and the framework is responsible for providing examples of these dependent items.The CDI framework is marked with the @Inject annotation to mark the dependent items that need to be injected, and use the context manager to find and provide these instances of these dependencies. Below is a simple example, demonstrating how to use the CDI framework to manage the dependence of components: public class UserService { @Inject private UserRepository userRepository; public void createUser(String username, String password) { User user = new User(username, password); userRepository.save(user); } } @ApplicationScoped public class UserRepository { public void save(User user) { // Save the user to the database } } public class Main { public static void main(String[] args) { Weld weld = new Weld(); WeldContainer container = weld.initialize(); UserService userService = container.instance().select(UserService.class).get(); userService.createUser("username", "password"); weld.shutdown(); } } In the above example, userService relies on UserRePOSITORY to save user information.By adding @inject annotations to the UserRePOSITORY field, the CDI framework will automatically injected it into the UserService instance. In the Main class, we initialize the CDI framework using the WELD container and obtain the userService instance by calling the container.instance (). Select (UserService.class) .get ().We can then use this instance to call the CreateUser method to create a new user. This is just a simple example. The CDI framework also provides many other functions, such as life cycle management, event trigger and interceptor.By using the CDI framework, developers can easily manage and maintain components in Java applications.