log4j

读log4j介绍的几点
1、Named Hierarchy
A logger is said to be an ancestor of another logger if its name followed by a dot is a prefix of the descendant logger name. A logger is said to be a parent of a child logger if there are no ancestors between itself and the descendant logger.
2、Level Inheritance
The inherited level for a given logger C, is equal to the first non-null level in the logger hierarchy, starting at C and proceeding upwards in the hierarchy towards the root logger.
3、Appender Additivity
The output of a log statement of logger C will go to all the appenders in C and its ancestors. This is the meaning of the term "appender additivity".

However, if an ancestor of logger C, say P, has the additivity flag set to false, then C's output will be directed to all the appenders in C and it's ancestors upto and including P but not the appenders in any of the ancestors of P.

Loggers have their additivity flag set to true by default.
4、提高log效率
logger.debug("Entry number: " + i + " is " + String.valueOf(entry[i]));
用if(logger.isDebugEnabled() {
        logger.debug("Entry number: " + i + " is " + String.valueOf(entry[i]));
      }替代