Open Services Gateway initiative - OSGi

Giriş

OSGi ile tam denk olmayan ancak biraz benzer özellikler veren ServiceLoader yazısına bakabilirsiniz.

OSGi Nedir?

Açıklaması şöyle. OSGi bir container üzerinde çalışır.

The OSGi framework is a standardized module system and service platform for the Java programming language. The OSGi standards has both open-source and commercial implementations. Below are some popular open source implementations of OSGi.

- Apache Felix

- Eclipse Equinox

Any OSGi application runs on any of above OSGi container and application will be developed as a Module/Plugins.

Maven

Şu satırı dahil ederiz

<dependency>
  <groupId>org.osgi</groupId>
  <artifactId>org.osgi.core</artifactId>
  <version>${osgi.version}</version>
  <scope>provided</scope>
</dependency>

Container için org.apache.felix plugin dahil edilir.

BundleActivator Sınıfı

Plugin'leri register etmek içindir.

Örnek

Şöyle yaparız

import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;

public class Activator implements BundleActivator {

  public static BundleContext bundleContext;

  @Override
  public void start(BundleContext context) throws Exception {
    bundleContext = context;
    registerServices();
  }

  @Override
  public void stop(BundleContext context) throws Exception {
    bundleContext = null;
  }

  private void registerServices() {
    CalculatorService service = new SubService();
    bundleContext.registerService(CalculatorService.class.getName(), service,
      new Hashtable<String, Object>());
  }
}

BundleContext Sınıfı

Eğer SpringBoot ile kullanıyorsak ConfigurableApplicationContext ile aynı şeydir.

Örnek

Şöyle yaparız

import org.osgi.framework.BundleContext;

import com.finalhints.osgi.Activator;
import com.finalhints.osgi.api.CalculatorService;

@RestController
@RequestMapping("/calculator")
public class CalculatorController {

  @GetMapping
  public List<String> getAllOperations() {
    BundleContext bundleContext = ...;

    try {
      Collection<ServiceReference<CalculatorService>> references = bundleContext
        .getServiceReferences(CalculatorService.class, null);
      for (ServiceReference<CalculatorService> reference : references) {
        CalculatorService calcService = bundleContext.getService(reference);
				
      }
    } catch (Exception e) {
	...
    }
    ...	
  }
}