[logback-user] Custom appender

[Frank Grimm]

Dear mailing list,

I'm trying to use logback (via its slf4j API) in an Eclipe/OSGi 
environment. More specifically I'm trying to write a logback appender 
that redirects log events to the Eclipse logging mechanism 
(org.eclipse.core.runtime.ILog).

So the first thing I did was to create an Eclipse plugin/PDE project for 
the custom appender. In the project, the following class was added:

package logback.eclipseappender;

import ch.qos.logback.core.AppenderBase;

public class EclipseAppender extends AppenderBase<Object> {
	@Override
	protected void append(Object eventObject) {
		// TODO
	}
}

The a logback configuration that made use of the custom appender was 
added to the project, too:

<configuration>
	<appender
		name="eclipse"
		class="eclipseappender.EclipseAppender">
		<layout class="ch.qos.logback.classic.PatternLayout">
			<Pattern>%d %p %t %c - %m%n</Pattern>
		</layout>
	</appender>
	
	<root level="debug">
		<appender-ref ref="eclipse"/>
	</root>
</configuration>

When the custom appender plugin/bundle is started in a new Eclipse 
runtime environment, the appender's class cannot be found (see 
stacktrace below).

I've read in another post (DynamicClassLoadingException - How does class 
loading in logback works?) that logback might require the logback jar 
files and the custom appender jar file to be bundled together. But 
bundling them does not make sense in OSGi environments since single 
bundles for each of logback's components (core, classic, slf4j API) and 
custom appenders should be used.

Is there a way to make logback see the appender class event if it's in 
another jar/bundle?

Thanks,
Frank

11:00:58,210 |-INFO in ch.qos.logback.core.joran.action.AppenderAction - 
About to instantiate appender of type [eclipseappender.EclipseAppender]
11:00:58,211 |-ERROR in ch.qos.logback.core.joran.action.AppenderAction 
- Could not create an Appender of type 
[eclipseappender.EclipseAppender]. 
ch.qos.logback.core.util.DynamicClassLoadingException: Failed to 
instantiate type eclipseappender.EclipseAppender
	at ch.qos.logback.core.util.DynamicClassLoadingException: Failed to 
instantiate type eclipseappender.EclipseAppender
	at 	at 
ch.qos.logback.core.util.OptionHelper.instantiateByClassName(OptionHelper.java:53)

[...]

Caused by: java.lang.ClassNotFoundException: eclipseappender.EclipseAppender
	at 	at 
org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:506)
	at 	at 
org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:422)
	at 	at 
org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:410)
	at 	at 
org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.loadClass(DefaultClassLoader.java:107)
	at 	at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
	at 	at 
ch.qos.logback.core.util.OptionHelper.instantiateByClassName(OptionHelper.java:45)
	at 	... 52 common frames omitted