The dynamic loading and loading mechanism in the OSGI service ServiceLoader framework
The dynamic loading and loading mechanism in the OSGI service ServiceLoader framework
Overview:
In OSGI (open service gateway initiative), ServiceLoader is a mechanism for loading and using services.Serviceloader allows developers to dynamically discover and load services provided in the OSGI runtime environment.This article will introduce the dynamic loading and loading mechanism of the OSGI service ServiceLoader framework, and provide relevant Java code examples.
1. The basic concept of the ServiceLoader framework
The ServiceLoader framework provides a simple and flexible way to discover and use services registered in the environment of OSGI.It uses Java's SPI (Service Provider Interface) mechanism and can dynamically load the services provided by it at runtime.The following is the basic concept of the ServiceLoader framework:
1. Service Interface: The service interface defines the communication protocol between the service user and the service provider.
2. Service Provider Interface: The service provider interface is an implementation interface for the service. The service provider needs to implement the interface to register the service from OSGI.
3. Service Provider: Service providers are the class or objects of the service provider interface.
4. Service Consumer: The service user discovers and uses the service class or objects by using the ServiceLoader framework.
How to use the ServiceLoader framework
Below is a basic step to use the ServiceLoader framework:
1. Create service interface:
First of all, you need to define a service interface, which will define the communication protocol between service users and service providers.
public interface GreetingService {
void greet(String name);
}
2. Create service provider:
Next, you need to create one or more service providers to realize the service provider interface.
public class EnglishGreetingService implements GreetingService {
@Override
public void greet(String name) {
System.out.println("Hello, " + name + "!");
}
}
public class ChineseGreetingService implements GreetingService {
@Override
public void greet(String name) {
System.out.println ("Hello," + name + "!"););
}
}
3. Registration service provider:
You need to register the service provider in the OSGI running environment.This can create a file called the service interface by creating a file called the service interface in the Meta-INF/Services directory and list the name of the service provider in the file.
For example, create a file called "My.package.greetingService" in the project's Meta-INF/Services directory, and add the following content to the file:
my.package.EnglishGreetingService
my.package.ChineseGreetingService
4. Use the ServiceLoader framework:
Now you can use the ServiceLoader framework in the service user to discover and use the service.
import java.util.ServiceLoader;
public class GreetingServiceConsumer {
public static void main(String[] args) {
ServiceLoader<GreetingService> serviceLoader = ServiceLoader.load(GreetingService.class);
for (GreetingService greetingService : serviceLoader) {
greetingService.greet("John");
}
}
}
In the above example, we use the serviceLoader.load () method to load the designated service interface.We can then use Foreach to traverse the ServiceLoader instance and call the Greet () method to use the service.
3. Dynamic loading and loading mechanism of the ServiceLoader framework
The Serviceloader framework uses the Java SPI mechanism, which allows dynamically loading services provided during runtime.In the OSGI environment, the ServiceLoader framework combines OSGI's modularity characteristics to realize the mechanism of dynamic loading and loading services.
When OSGI runs the environment, it scans and loads all modules and check whether there is a file of the service interface in each module in the Meta-INF/Services directory in each module.OSGI will then dynamically load and register these service providers based on the service providers listed in the file.This allows service providers to add or delete dynamically at runtime.
The ServiceLoader framework provides the following methods to dynamically discover and load services during runtime:
1. public static <S> ServiceLoader<S> load(Class<S> service)
This method is used to load all service providers in the designated service interface.It returns a ServiceLoader instance for iterating all the loaded service providers.
2. public static <S> ServiceLoader<S> load(Class<S> service, ClassLoader loader)
This method is similar to the first method, but allows a ClassLoader to load the service interface service provider.
3. public Iterator<S> iterator()
This method is used to iterate the ServiceLoader instance in order to access the loaded service providers.
Fourth, summary
In the OSGI service ServiceLoader framework, dynamic loading and loading mechanisms are realized through the Java SPI mechanism and OSGI's modularity features.The ServiceLoader framework allows dynamically discover and load service providers during runtime, so that developers can flexibly use services.By following the above usage methods and related APIs, developers can easily use the ServiceLoader framework to realize the dynamic loading and loading of services in the OSGI environment.
Code example: https://gist.github.com/12BD7A2203D3F9DF5F4D749747B09425
