CDI API tutorial: dependency injection in Java class library
CDI API tutorial: dependency injection in Java class library
In modern software development, dependency injection is a commonly used design mode, which can simplify the writing and maintenance of the code and promote the software architecture of loose coupling.On the Java platform, Contexts and Dependency Injection (CDI) API is a set of powerful tools to achieve dependency injection and context management.
Dependent injection is a method of decoupling by hard -coding dependence from the code.Instead, dependencies are dynamically injected into the code through external containers (such as CDI containers).This method makes the replacement, configuration and test of components easier.In the CDI, the dependency is declared by @Inject annotation.
The following is a simple example, demonstrating how to use dependency injection in the CDI:
First, we define an interface GreetingService:
public interface GreetingService {
String greet();
}
Then, we created a class that implemented the GreetingService interface:
@ApplicationScoped
public class EnglishGreetingService implements GreetingService {
@Override
public String greet() {
return "Hello!";
}
}
Then, we use dependency injection in another class:
@RequestScoped
public class GreetingController {
@Inject
GreetingService greetingService;
public String getGreeting() {
return greetingService.greet();
}
}
In this example, the GreetingService field in the GreetingController class is injected through the @Inject annotation.The CDI container will be responsible for instantiated and managing GreetingService and injected it into the GreetingController.
Finally, we can use GreetingController at the entrance point of the application:
public class Main {
public static void main(String[] args) {
Weld weld = new Weld();
WeldContainer container = weld.initialize();
GreetingController greetingController = container.select(GreetingController.class).get();
String greeting = greetingController.getGreeting();
System.out.println(greeting);
weld.shutdown();
}
}
In this example, we initialize the CDI container using the WELD framework and obtain an instance of the GreetingController in the fairy container.We then call the getGreeting method to get greetings and print it to the console.
The CDI API provides many functions, such as life cycle management, cycle dependency analysis, event notice, etc.By using CDI, we can better organize code and improve the scalability and maintenance of the software.
This article provides a simple CDI dependency injecting tutorial, introducing the basic concepts and usage of CDI.By using CDI, we can easily handle dependencies and build a highly configurable and tested Java application.
Note: In actual development, you may need to configure CDI containers and define more annotations and rules to meet your specific needs.The examples provided here are only used to demonstrate the basic concepts and usage.
I hope this article will help you understand that CDI dependency injection is helpful!
