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
/**
	 * Disposes all resources and reset.
	 */
	public static void dispose( )
	{
		isInitContext = false;
		for ( int i = 0, n = sessionIds.size( ); i < n; i++ )
		{
			String sessionId = (String) sessionIds.get( i );
			clearSessionFiles( sessionId );
		}
		sessionIds.clear( );
	}
	/**
	 * Clear the temp files when session is expired
	 * 
	 * @param id
	 *            session id
	 */
	public static void clearSessionFiles( String id )
	{
		if ( id == null )
		{
			return;
		}
		
		String tempFolder = imageFolder + File.separator + id;
		File file = new File( tempFolder );
		deleteDir( file );
	}