Register a Log Service with a Component

Purpose

Show how to register a service with a component.

Prerequisites

• Declarative services - org.osgi.service.component
• Log Service - org.osgi.service.log
• osgi interfaces, provides all service interfaces for the OSGi specifications.

Instructions

Components use POJOs: simple objects that are not hindered by any framework code. In this snippet we can actually use the same code as in the RegisterService snippet.

  Source:  aQute.servicecomponent.SimpleLogService
  package aQute.servicecomponent;

  import org.osgi.framework.*;
  import org.osgi.service.log.*;

  public class SimpleLogService implements
      org.osgi.service.log.LogService {


    public void log(int level, String message) {
      log(level, message, null);
    }

    public void log(int level, String message,
        Throwable exception) {
      System.err.println(level(level) + ":" + message + ":"
          + exception);
    }

    public void log(ServiceReference sr, int level,
        String message) {
      log(sr, level, message, null);
    }

    public void log(ServiceReference sr, int level,
        String message, Throwable exception) {
      System.err.println(level(level) + ":"
          + sr.getProperty(Constants.SERVICE_ID) + ":"
          + message + ":" + exception);
    }

    private String level(int level) {
      switch (level) {
      case LogService.LOG_DEBUG:   return "DEBUG";
      case LogService.LOG_ERROR:   return "ERROR";
      case LogService.LOG_INFO:    return "INFO";
      case LogService.LOG_WARNING: return "WARNING";
      default:  return "UNKNOWN(" + level + ")";
      }
    }
  }

There is no need for an activator because we use Declarative Services. The only thing we therefore need is Bnd:

  Bnd:  aQute.servicecomponent
  Export-Package: aQute.servicecomponent
  Service-Component: aQute.servicecomponent.SimpleLogService; \ 
    provide:=org.osgi.service.log.LogService; \ 
    properties:="service.pid=biz.aQute.servicecomponent, \ 
        service.ranking=2000"

Links

• The specification discusses declarative services in chapter 112 of the OSGi Compendium.
• Declarative Services Javadoc
• Log Service Javadoc
• aQute.servicecomponent.jar