Bug 193467 URL hyperlink can't work in chart viewer
chart/org.eclipse.birt.chart.viewer/src/org/eclipse/birt/chart/viewer/internal/util/ChartImageManager.java
public String getAbsoluteImageFolder( )
	{
		return imageFolder + File.separator + sessionId;
	}
	public String getRelativeImageFolder( )
	{
		return IMAGE_FOLDER + "/" + sessionId; 
	}
	/**
	 * Deletes all files and subdirectories under dir. Returns true if all
	 * deletions were successful. If a deletion fails, the method stops
	 * attempting to delete and returns false.
	 */
	private static boolean deleteDir( File dir )
	{
		if ( dir.isDirectory( ) )
		{
			String[] children = dir.list( );
			for ( int i = 0; i < children.length; i++ )
			{
				boolean success = deleteDir( new File( dir, children[i] ) );
				if ( !success )
				{
					return false;
				}
			}
		}
		
		System.out.println( "Cleaned file: " + dir.getPath( ) ); 
		return dir.delete( );