java: Why Log4J's Logger should be declared static final

Declaring Logger to be static final is recommended, particularly for long lived objects such as the Struts Action class
http://www.owasp.org/index.php/Poor_Logging_Practice:_Logger_Not_Declared_Static_Final

e.g. private static final Logger LOGGER = Logger.getLogger(Donkey.class)

The Struts framework creates only one instance of an Action class for all client requests. e.g. FooAction and BarAction will only be created once.
Static means the Logger is not specific to a particular client request, but is shared by all requests.
Final means the Logger will only be instantiated once.

Logger is tread safe because it doesn't hold a state.