[osgi logging] part 6 – how to start the logging framework

This is part 6 of my blogseries about ‘Logging in OSGI Enterprise Applications‘ – you’ll find all parts here.

Normaly you put your needed bundles into the Dropins folder from your IDE (if there’s no update site) or add them to your Target Platform definition and you’re done.

Integrating a Logging Framework there are some requirements:

• you want to get all logged messages from the beginning, so logging bundles have to start early
• you want to control that your bundles are used and not others providing the same packages

You should always carefully think about using Start-Levels, but in this case it makes sense.

If you followed my blog series about Target Platform, then you know that its important to distinguish between IDE and Runtime (Target Platform).

Starting Logging Framework from OSGI Runtime

In most cases you’re interested into the Runtime only, because you want to know what your running product is logging.

Since Galileo you can define the Start-Level in the Product Configuration file:

– same way as from an OSGI Launch Configuration:

or from an Eclipse Application Configuration:

Youl’ll find the setting of Start-Level and Auto-Start under different Tabs and named Plug-Ins or Bundles, but its always the same 😉

Hint: The Auto-Start “default” depends from your setting of “Default Auto-Start” as false or true. If you want to be sure that the right value was choosen you should explicit set to true or false at each bundle.

Here are the settings to autostart the Logging Framework early from your Runtime Product / OSGI Launch / Application Launch:

per ex. Default Auto-Start Level 3

• org.eclipse.osgi: Start-Level -1, Auto-Start true
• org.eclipse.equinox.common: Start-Level 2, Auto-Start true
• org.eclipse.equinox.ds: Start-Level default, Auto-Start true
• all logging framework bundles: Start-Level 2, Auto-Start true
• org.ekkescorner.logging bundles: Start-Level 2, Auto-Start true
• all other bundles: Start-Level default, Auto-Start default

what happens:

1. Start-Level -1: Equinox OSGI Runtime starts at first
2. Start-Level 2: equinox.common and all logging bundles are started
   1. org.ekkescorner.logging.starter.runtime (Bundle-ActivationPolicy: lazy)
      1. Avtivator start() calls SLF4JBridgeHandler.install() – this causes bundle ‘jul.to.slf4j’ to catch all java.util Logging
      2. logs a message: logger.debug(Activator.bundleMarker, “SLF4JBridgeHandler started”) – this causes slf4j and logback to begin initialization, read the config and perhaps log something
3. Start-Level default: all bundles with Auto-Start true are started
   1. org.eclipse.equinox.ds is auto-started
      1. analyzes the DS Component from org.ekkescorner.logging.starter.runtime
      2. if LogReaderServices or ExtendedLogReaderServices become available, our LogListeners will get the LogEntries
   2. other bundles are started if needed and because SLF4J / Logback is initialized all dependencies to logging packages are resolved from SLF4J / Logback and all log messages are catched

Starting Logging Framework from IDE

In some cases you may have the need to log from your running IDE and it should work simply adding some bundles.

Adding bundles to Dropins folder or updating from Update Sites there’s no easy way to set Start-Level or Auto-Start.

Above you have seen how we solve this with the org.ekkescorner.logging.starter.runtime bundle at Runtime

– for the IDE we use another Bundle: org.ekkescorner.logging.starter.ide (Bundle-ActivationPolicy: lazy)

the important part – we have to use the Extension Point org.eclipse.ui.startup to get the bundle early started:

the Class AutoStartLogging has to implement org.eclipse.ui.IStartup

import org.eclipse.ui.IStartup;
import org.ekkescorner.logging.starter.ide.Activator;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.bridge.SLF4JBridgeHandler;

public class AutoStartLogging implements IStartup {

	// logger name = class name
	private static final Logger logger = LoggerFactory.getLogger(AutoStartLogging.class);

	public void earlyStartup() {

		logger.info(Activator.bundleMarker, "earlyStartup slf4j SLF4JBridgeHandler..."); //$NON-NLS-1$	

		// route java.util.logging to slf4j
		SLF4JBridgeHandler.install();

		logger.debug(Activator.bundleMarker, "SLF4JBridgeHandler started"); //$NON-NLS-1$

	}
}

You need this bundle only if you really have to receive log messages from the bundles of your running IDE.

One of my use-cases is the development and test of the redView WYSIWYG Designer – Editor where it’s great to get logging messages from the redView Designer bundles.
you’ll find the overview of this blog series here. stay tuned… part7 follows…