OSGi Console Logger

Logging in OSGi can be very tedious. OSGi provided a very robust framework for logging but it misses one point:

And this is where OSGi misses the point with its very sophisticated framework. There is a framework but there is no implementation of the last link in the chain: the output of the log.

Logging should be dead simple. But in OSGi it just isn't that simple. There is the LogService, the LogReader and the LogListener … and the whole time I just think “Hey, I just want to output some messages!”

Both popular OSGi frameworks (Eclipse Equinox and Apache Felix) have implementation for LogService and LogReader but the LogListener is not implemented for the end-user (the application developer).

So here is a trivial implementation of a LogListener , using System.out:

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.osgi.service.log.LogEntry;
import org.osgi.service.log.LogListener;
import org.osgi.service.log.LogReaderService;
import org.osgi.service.log.LogService;

public class ConsoleLogListener implements LogListener {

	private static final String LOG_LEVEL_INFO = "INFO ";
	private static final String LOG_LEVEL_WARN = "WARN ";
	private static final String LOG_LEVEL_ERROR = "ERROR";
	private static final String LOG_LEVEL_DEBUG = "DEBUG";

	private static final String[] LOG_LEVELS = { 
		LOG_LEVEL_ERROR, LOG_LEVEL_WARN, LOG_LEVEL_INFO, LOG_LEVEL_DEBUG 
	};

	private DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

	private int logLevel = LogService.LOG_INFO;

	public void bindLogReader(LogReaderService logReader) {
		logReader.addLogListener(this);
	}

	public void unbindLogReader(LogReaderService logReader) {
		logReader.removeLogListener(this);
	}

	@Override
	public void logged(LogEntry entry) {
		if (!isLoggable(entry)) {
			return;
		}

		String message = formatLogTime(entry.getTime()) + " " + formatLogLevel(entry.getLevel())
				+ " - " + entry.getBundle().getSymbolicName() + " - " + entry.getMessage();

		if (entry.getServiceReference() != null) {
			message = message + " - [ " + entry.getServiceReference().getClass().getName() + " ("
					+ entry.getServiceReference().getProperty("service.id") + ") ]";
		}
		
		System.out.println(message);
	}

	private String formatLogTime(long time) {
		return dateFormat.format(new Date(time));
	}

	private String formatLogLevel(int logLevel) {
		return LOG_LEVELS[--logLevel];
	}

	private boolean isLoggable(LogEntry entry) {
		boolean loggable = false;

		if (logLevel <= entry.getLevel()) {
			loggable = true;
		}

		return loggable;
	}

}

But that isn't doing the trick yet as it is nowhere registered in the logging framework. The easiest way to register it is to make a declarative component of it and bind the LogReader implementations to it, file OSGI-INF/service-log.xml.

<?xml version="1.0" encoding="UTF-8"?>
<scr:component xmlns:scr="http://www.osgi.org/xmlns/scr/v1.1.0" immediate="true" name="miworkplace.log.console">
   <implementation class="miworkplace.log.ConsoleLogListener"/>
   <reference bind="bindLogReader" cardinality="0..n" interface="org.osgi.service.log.LogReaderService" name="LogReaderService" policy="dynamic" unbind="unbindLogReader"/>
</scr:component>

Service-Component: OSGI-INF/service-log.xml