In -depth understanding of the implementation principle of CDI API

In -depth understanding of CDI (context and dependency injection) API implementation principle Overview: CDI (Contexts and Dependency Injection) is a Java EE specification that is used to manage the life cycle and dependencies injection of the person.The CDI API provides a set of mechanisms and annotations that enable developers to more easily write scalable, loose coupling and test -available code.This article will explore the implementation principles of the CDI API and provide some related Java code examples. CDI API's core concept: 1. Contexts: The context refers to the life cycle and visibility of the object.In the CDI, there are different contexts, such as application context, context of session, request context, etc.Each context has its own life cycle, and uses the corresponding context manager to manage. 2. Bean Candidate: Candidate category refers to a class that can be managed and injected by the CDI container.You can mark it as a candidate by using related notes (such as@javax.enterprise.inject.default or@javax.inject.named) as a candidate class. 3. Qualifier: Limited symbols are used to refine the type of dependent injection.By using@javax.inject.qualifier annotations to define limited marks, you can accurately select specific dependencies as needed. 4. Producer Method: The producer method is used to create examples of candidate.By using the@javax.enterprise.inject.produces annotation, mark a method as a producer method, so as to tell the CDI container to use this method when this instance is needed. 5. Event: The event is used to communicate between different parts of the application.By using@javax.nterprise.event.event definition events, and using @Inject to inject an Event instance to trigger an event or monitoring event. Principles of CDI API: The implementation principle of the CDI API can be summarized as the following steps: 1. Load and initialize the CDI container: CDI container is the core component of the CDI API. It is responsible for the life cycle and dependency injection of the management object.When the application starts, the CDI container will be loaded and initialized all the CDI -managed classes, including candidate and producer methods. 2. Create and destroy objects: CDI containers will create and destroy objects as needed.When a candidate is needed, the CDI container uses appropriate contextors to create an instance of this class and destroy the instance at the end of the context to ensure that the life cycle of the object is managed. 3. Treatment dependencies injection: When a dependencies need to be injected, the CDI container will find the matching candidate class and inject the practical example into the target class.CDI uses a limited character information provided by programmers to select the correct dependence. 4. Event notification: CDI containers allow different parts of the application to communicate through the event.When an event is triggered, the CDI container will notify all the categories of the incident and pass the incident instance to them. Example code: Below is a simple example, demonstrating how to use CDI API to manage the life cycle and dependency injection of the object. First, define a candidate: import javax.inject.Named; import javax.enterprise.context.RequestScoped; @Named @RequestScoped public class User { private String name; // Getter and setter methods } Then, create a producer method: import javax.enterprise.inject.Produces; public class UserProducer { @Produces public User createUser() { return new User(); } } Finally, dependencies injected in the class that needs to be used in the User instance: import javax.inject.Inject; public class UserService { @Inject private User user; // Use other methods of using User instance } In the above examples, the CDI container will automatically create a User instance when needed and inject it into userService. in conclusion: The CDI API provides an elegant and flexible way to manage the life cycle and dependency injection of the object.Through in -depth understanding of the implementation of the CDI API, developers can better use CDI to create scalable, loose coupling, and testable Java EE applications.I hope this article will help you understand the implementation principle of the CDI API!