Java class library Annotations for DS framework technical analysis
Java class library Annotations for DS framework technical analysis
Overview
Annotations for DS (Dependency Injection Annotations for Declarative Services) is a Java library to simplify the dependency injection in Declarative Services (DS).Declarant Services is part of OSGI (Open Service Gateway Initiative) specification. It provides a mechanism for dynamic service registration and dependencies for dynamic modular applications.Annotations for DS provides a method of using annotations to make developers more conveniently define and manage the dependence between management components.
The working principle of Annotations for DS
Annotations for DS provides a simple way to define and manage the dependent relationship between DS components by using the Java annotation method to embed the dependency relationship between DS components.This type of library provides the following annotations:
@Component: Used to mark a class as a DS component.
@Service: Used to mark a class as a service, you can provide specific functions through this service.
@Reference: Used to mark a variable as a reference to a service to achieve dependence injection.
@Activate: The method that needs to be executed when the component is activated.
@Modify: The method that needs to be executed when the component is modified.
@DeaCTIVATE: The method that needs to be executed when the component is discontinued.
For example code
Below is an example code using Annotations for DS:
@Component
public class MyComponent {
@Reference
private MyService myService;
@Activate
public void activate() {
// The code executed when the component active
}
@Modified
public void modified() {
// The code executed when the component is modified
}
@Deactivate
public void deactivate() {
// The code executed when the component is discontinued
}
}
In the above code,@Component annotation marks the Mycomponent class as a DS component.@Reference annotation marks the MyService field as a reference to the MyService service, so that the field can obtain an instance of MyService through dependency injection.@Activate,@MODIFIED, and @DeaCTIVATE annotations are marked with the corresponding code in different stages of the component life cycle in different stages of component life cycle.
Related configuration
In order to enable Annotations for DS, it is necessary to perform related configuration in the configuration file of the project.The following is an example configuration file (take Maven project as an example):
<build>
<plugins>
<plugin>
<groupId>org.apache.felix</groupId>
<artifactId>maven-scr-plugin</artifactId>
<version>1.23.0</version>
<executions>
<execution>
<id>generate-scr-scrdescriptor</id>
<goals>
<goal>scr</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
In the above configuration, the Apache Felix Maven SCR plug -in is used to generate the description file of the DS component.This file describes the dependencies between DS components, and the container is used during supply.
Summarize
Annotations for DS provides developers with a simple and powerful way to manage the dependent relationship between DS components.Through Annotations for DS, you can use annotations to mark components and dependencies in the code without manually writing tedious description files.This enables developers to focus more on the realization of business logic and improve development efficiency.
