aQute | Snippets / Register a Log Service with a Bundle Activator

Purpose

Show the simplest bundle that registers a service. This is demonstrated with a component as well as the classic Bundle Activator way.

Prerequisites

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

Instructions

We first create a Log Service implementation class. For simplicity, we only implement the Log Service, and not the Log Reader Service.

Implementation is really simple, we log to the console:

 Source: aQute.registerservice.SimpleLogService
 package aQute.registerservice;
 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 + ")";
    }
  }
 }

The SimpleLogService must be registered with the OSGi service registry. This requires a BundleContext object; this object is handed over to a Bundle Activator. The following code therefore shows the bundle activator that registers the service.

 Source: aQute.registerservice.RegisterService
  package aQute.registerservice;  
  import java.util.*;
  import org.osgi.framework.*;
  import org.osgi.service.log.*;

  public class RegisterService implements BundleActivator {
    ServiceRegistration registration;

    public void start(BundleContext context) throws Exception {
      Hashtable properties = new Hashtable();
      properties.put(Constants.SERVICE_PID,
          "biz.aQute.snippet.registerservice");
      properties.put(Constants.SERVICE_DESCRIPTION,
          "Simplistic log service that logs to console out. "
              + "Will not dispatch to LogReader services");
      properties.put(Constants.SERVICE_VENDOR, "aQute");
      properties.put(Constants.SERVICE_RANKING, new Integer(
          1000));
      registration = context.registerService(LogService.class
          .getName(), new SimpleLogService(), properties);
    }

    public void stop(BundleContext context) throws Exception {
    // automatically unregistered
    }
  }

Notice that it is not necessary to unregister the service. After the stop method is called, the service is automatically unregistered.

To put it all together

  Bnd: aQute.registerservice.bnd
  Export-Package: aQute.registerservice
  Bundle-Activator: aQute.registerservice.RegisterService

Purpose

Prerequisites

Instructions

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