CDI API annotation analysis and examples
CDI API (context and dependency injection) is a specification in Java EE, which is used to manage the dependency relationship between objects.CDI provides a set of annotations to define and analyze dependencies in injection, thereby simplifying the dependency injection in the Java application.
The core annotation of CDI API includes:
1. @Inject: Used to mark fields, construct functions or methods that need to be injected.When the Java container initializes an object, it automatically finds appropriate instances to meet these dependencies.
2. @qualifier: Used to refine the choice of relying on injection.Generally, when there are multiple instances to implement the same interface, using this annotation can clearly specify the instance to be injected.
3. @producess: Used to declare a method that generates an example of a specific type of type.The CDI container can use this method to create instances and automatically inject it where the need.
4. @Dependent: It is used to define the default dependencies.This scope indicates the same life cycle that depends on its object.
5. @ApplicationScoped: It is used to define a single object of an application level.The object is unique during the life cycle of the application.
Here are some examples of CDI API:
@ApplicationScoped
public class DatabaseService {
public void connect() {
// The code connected to the database
}
}
@Qualifier
@Retention(RUNTIME)
@Target({ METHOD, FIELD, PARAMETER})
public @interface Production {
}
@Produces
@Production
public DatabaseService createDatabaseService() {
return new DatabaseService();
}
public class ExampleService {
@Inject
private DatabaseService databaseService;
public void performAction() {
databaseService.connect();
// Execute other operations
}
}
In the above examples, `databaseService` is a single -example object of an application level. The`@ApplicationScoped` annotation is used to mark.`CreateDataBaseService` Methods using`@Produces` and@Production` Annotation declares an instance of a method -level producer for creating a `DataBaseService`.`Exampleservice` Class uses`@inject` Note to inject the `databaseService` into the` DataBaseService` field, and use the field to connect the database in the `Performaction` method.
The annotations and specifications of the CDI API provide a flexible method that simplifies the injecting injects, making the development of Java applications more simple and maintainable.By using these annotations, developers can easily manage the dependence between objects and improve the reuse and testability of code.
