Bug 165188 logging per report
Setting up a dedicated (birt) report server, which serves all our web apps, leads to a logging desaster. Birtegine logs all messages to one file. There's no info which rptdesign caused the logmessage or who (e.g. user) caused the logmessage. Retrieving who/which rpt caused some logmessage is not possible! There are two possible solutions: (a) prefixing each logmessage with a userdefineable message (task.setLogprefix("myprefix")) (b) set an outputstream for each task (task.setLoggingOutputStream(outputstream)) to split the huge logfile to many small pieces.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/EngineLogger.java
}
	/**
	 * Change the log level to the newLevel
	 * @param newLevel - new log level
	 */
	public static void changeLogLevel( Level newLevel )
	{
		Logger logger = Logger.getLogger( BIRT_NAME_SPACE );
		assert (logger != null);
		if ( newLevel != null )
		{
			if ( Level.OFF == logger.getLevel( ) && Level.OFF != newLevel )
			{
				createLogFile( logger );
			}
			logger.setLevel( newLevel );
		}
	}
	
	/**
	 * This is a utility function that will create an unique file name with the timestamp information in the file name and
	 * append the file name into the directory name.
	 * For example, if the directory name is C:\Log, the returned file name will be C:\Log\ReportEngine_2005_02_26_11_26_56.log.
	 * @param directoryName - the directory name of the log file. 
	 * @return An unique Log file name which is the directory name plus the file name.
	 */
	private static String generateUniqueLogFileName( String directoryName )
	{
		SimpleDateFormat df = new SimpleDateFormat("yyyy_MM_dd_HH_mm_ss"); 
		String dateTimeString = df.format( new Date() );