Dependency Manager - Adapter

Adapters, like aspects, are used to "extend" existing services, and can publish different services based on the existing one. An example would be implementing a management interface.

An adapter will be applied to any service that matches the specified interface and filter. For each matching service an adapter will be created based on the adapter implementation class. The adapter will be registered with the specified interface and existing properties from the original service plus any extra properties you supply here. It will also inherit all dependencies, and if you declare the original service as a member it will be injected.

To define an adapter component, you need to create an AdapterComponent component using the DependencyActivatorBase.createAdapterComponent() or the DependencyManager.createAdapterComponent() method. This interface extends the Component interface in order to add extra setters methods needed to define an adapter service component.

Usage example

Here is a sample showing a HelloServlet adapter component which creates a servlet each time a HelloService is registered in the osgi service registry with the "foo=bar" service property.

 public class Activator extends DependencyActivatorBase {
     &Override
      public void init(BundleContext context, DependencyManager dm) throws Exception {
          Component adapterComponent = createAdapterComponent()
              .setAdaptee(HelloService.class, "(foo=bar)")
              .setInterface(HttpServlet.class.getName(), null)
              .setImplementation(HelloServlet.class);
          dm.add(adapterComponent);
      }
 }

public interface HelloService {
    String sayHello();
}

public class HelloServlet extends HttpServlet {
    volatile HelloService adatpee; // injected

    void doGet(HttpServletRequest req, HttpServletResponse resp) {
        ...
        resp.getWriter().println(adaptee.sayHello());
    }
}