How to use the OSGI service ServiceLoader framework for component development
Use the OSGI service ServiceLoader framework for component development
Overview:
In componential development, we usually split systems into multiple components that can be deployed independently and collaborate through interfaces.In the OSGI (Open Service Gategory Agreement), we can use the ServiceLoader framework to achieve component development.ServiceLoader is a standard library of Java, which allows us to dynamically load and obtain the implementation of the service interface during runtime.This article will introduce how to use the OSGI service ServiceLoader framework for component development.
step:
1. Definition interface:
First, we need to define a service interface.Suppose we want to develop a graphical editor, we can first define a graphical interface (Shape).
public interface Shape {
void draw();
}
2. Implement interface:
After defining the interface, we can implement specific services according to business needs.In OSGI, each service needs to specify the interface and implement the associated relationship in the manifest.mf file.
public class Square implements Shape {
@Override
public void draw() {
System.out.println ("Draw a square");
}
}
public class Circle implements Shape {
@Override
public void draw() {
System.out.println ("Draw a circular");
}
}
3. Configure manifest.mf file:
Create a manifest.mf file in the root directory of the project, and configure the service interface and implement the association relationship.
Service-Component: OSGI-INF/*.xml
4. Create XML configuration file:
Create a configuration file called Shape.xml under the SRC/main/Resources folder, and add the service -related information to the file.Each service corresponds to a component element.
<?xml version="1.0" encoding="UTF-8"?>
<components xmlns="http://www.osgi.org/xmlns/scr/v1.2.0">
<component name="square" enabled="true" immediate="true" configuration-policy="require"
activate="activate" deactivate="deactivate">
<implementation class="com.example.Square"/>
<service>
<provide interface="com.example.Shape"/>
</service>
</component>
<component name="circle" enabled="true" immediate="true" configuration-policy="require"
activate="activate" deactivate="deactivate">
<implementation class="com.example.Circle"/>
<service>
<provide interface="com.example.Shape"/>
</service>
</component>
</components>
5. Use serviceLoader to load service:
Load the service of the specified interface with the static method of the ServiceLoader class.Through the service instance obtained by traversing, we can perform related operations.
public class Editor {
public static void main(String[] args) {
ServiceLoader<Shape> shapeLoader = ServiceLoader.load(Shape.class);
for (Shape shape : shapeLoader) {
shape.draw();
}
}
}
Run the main method of Editor, you can see that the output result is:
Draw a square
Draw a circle
Summarize:
By using the OSGI service ServiceLoader framework, we can achieve component development.First, define the interface and implement the interface according to business needs.Then, configure the associated relationship between the interface and implementation class in the Manifest.mf file, and create the XML configuration file.Finally, use the ServiceLoader class to load the service and conduct relevant operations by traversing the service examples obtained.In this way, we can easily achieve component development and can dynamically load and switch different services.
