Java CDI framework introduction and usage guide
Java CDI (Contexts and Dependency Injection) is a framework for managing dependency relationships and contexts.CDI provides a method of simplifying the Java development process by enabling dependency injection and context management functions in the Java EE application to simplify the Java development process.CDI is part of the Java EE 6 specification. It provides developers with a method defined by transplantable components and allows these components to deploy and operate in different Java EE containers.
The core concept of CDI includes context, scope, dependency injection and events.The context refers to the mechanism of the life cycle of managing objects in the application.CDI defines several different scope, including the scope of application, session range, scope of requests, and dependencies.These areas determine the visibility and life cycle of the object in different stages or contexts of the application.
The CDI framework realizes the dependent relationship management between objects by dependency injection.Developers can tell CDI containers to automatically inject the required dependencies by marking the solution (such as @Inject) where the dependent object is required.In this way, when running, the CDI container will automatically find and inject the corresponding dependencies.This method eliminates the tedious process of manual creation and management objects, and improves the readability and maintenance of the code.
In addition to relying on injection, CDI also provides event mechanisms to achieve decoupling between components.Developers can publish and monitor incidents to pass messages between components.Using the CDI event mechanism can easily realize the structure of loose coupling, and improve the flexibility and scalability of the code.
The following is an example of using the CDI framework to demonstrate how to define and use the injected bean:
import javax.inject.Inject;
@ApplicationScoped
public class GreetingService {
@Inject
private ConfigurationService configurationService;
public void greet() {
String greetingMessage = configurationService.getGreetingMessage();
System.out.println(greetingMessage);
}
}
@RequestScoped
public class ConfigurationService {
public String getGreetingMessage() {
return "Hello, world!";
}
}
public class Main {
public static void main(String[] args) {
GreetingService greetingService = CDI.current().select(GreetingService.class).get();
greetingService.greet();
}
}
In the above example, the GreetingService class depends on the ConfigurationService class.By using @Inject notes on the GreetingService field, the CDI container will automatically find and inject instances of ConfigurationService.We can then use the injecting dependency item by calling the Greet () method.
The use guide of the CDI framework is as follows:
1. In the POM.XML file of the Java EE project, add the dependency item of CDI, such as:
<dependency>
<groupId>javax.enterprise</groupId>
<artifactId>cdi-api</artifactId>
<version>2.0</version>
</dependency>
2. In the source code of the project, define and use the injected Bean using the annotation of the CDI framework.Common annotations include@ApplicationScoped,@RequestScoped,@Sessionscoped, etc.
3. Where to inject Bean, use @Inject annotation to tell the CDI container to automatically inject dependencies.
4. When the project starts, obtain an instance of the CDI container and use the selection () method to obtain the required bean instance.
5. Use the injected dependency item to execute business logic.
To sum up, CDI is a framework for managing dependency relationships and contexts in Java EE.By using CDI, developers can simplify the development process of Java applications and improve the readability and maintenance of code.I hope this article will help you understand the CDI framework and its use.
