The core concept and principle of OSGI API framework
OSGI (open service portal architecture) is a framework and specification for building scalability and modular applications.It provides a dynamic module system implementation that splits the application into small, autonomous modules. Each module can be installed, upgraded, uninstalled, and started independently.The core concept and principle of OSGI are the key to realizing this dynamic modularity.
1. Bundle: The basic components of OSGI applications are modules.It is an independent, reusable software component with its own class, resources and dependence.Each module describes its own attributes, dependencies and other metadata through a manifest file.
The following is a simple module example:
// MyModule.java
public class MyModule {
public void sayHello() {
System.out.println("Hello from MyModule!");
}
}
// Activator.java
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
public class Activator implements BundleActivator {
public void start(BundleContext context) throws Exception {
System.out.println("MyModule started!");
MyModule module = new MyModule();
module.sayHello();
}
public void stop(BundleContext context) throws Exception {
System.out.println("MyModule stopped!");
}
}
2. Framework: OSGI provides a modulework that is responsible for installing, starting, stopping and uninstalling the module.The module manager dynamically loads and uninstalls the module by managing the dependency between managing modules during the application, and provides running services.
The following is an example of installing and startup modules using the OSGI module manager:
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;
import org.osgi.framework.BundleException;
import org.osgi.framework.launch.Framework;
import org.osgi.framework.launch.FrameworkFactory;
import java.util.HashMap;
import java.util.Map;
public class OsgiApp {
public static void main(String[] args) throws Exception {
FrameworkFactory frameworkFactory = new org.apache.felix.framework.FrameworkFactory();
Map<String, String> config = new HashMap<>();
config.put("org.osgi.framework.storage.clean", "onFirstInit");
config.put("org.osgi.framework.bootdelegation", "*");
Framework framework = frameworkFactory.newFramework(config);
framework.start();
BundleContext context = framework.getBundleContext();
Bundle bundle = context.installBundle("file:/path/to/my-module.jar");
bundle.start();
// Do something with the module...
framework.stop();
framework.waitForStop(0);
}
}
3. Service: OSGI provides a dynamic service model. Through it, the module can provide functions in the form of service and use services provided by other modules.Services are the basic ways of communication and interaction between modules, and can be shared and used through interface definition and implementation.
Here are a simple service interface and implementation example:
// MyService.java
public interface MyService {
void doSomething();
}
// MyServiceImpl.java
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceRegistration;
public class MyServiceImpl implements MyService, BundleActivator {
private ServiceRegistration registration;
public void start(BundleContext context) throws Exception {
System.out.println("MyService started!");
registration = context.registerService(MyService.class.getName(), new MyServiceImpl(), null);
}
public void stop(BundleContext context) throws Exception {
System.out.println("MyService stopped!");
registration.unregister();
}
public void doSomething() {
System.out.println("MyService is doing something...");
}
}
The module using this service can be obtained and used in the following ways:
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
public class SomeModule {
public void doSomethingWithService(BundleContext context) {
ServiceReference<MyService> serviceRef = context.getServiceReference(MyService.class);
MyService service = context.getService(serviceRef);
service.doSomething();
// Release the service reference
context.ungetService(serviceRef);
}
}
Through these core concepts and principles, OSGI provides a flexible, scalable and modular development method to help developers build complex applications and solve the challenges of modular and dependent management.By dynamic module system, module manager and service model, developers can better manage the life cycle and dependency relationship of the application, realize the dynamic assembly and communication of the module, and improve the reliability and scalability of the application.
