Frankly, if a method is so complex that you feel the urge to depict it in UML, your best bet is to split it into several smaller methods.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus