Why is the logger (logger) declared as static final

(1) For the consideration of resource utilization, Logger's construction method parameter is class, which determines that logger is based on class structure to distinguish log, so a class as long as a logger can be, so static
(2) final represents a programming habit, indicating that the logger of the class only records the information of the class, otherwise the log will not be able to provide a convincing record

By the way, stick to one of your own log4j.properties:

Log4j.rootlogger=info,console

Log4j.appender.console=org.apache.log4j.consoleappender
Log4j.appender.console.target=system.out
log4j.appender.console.layout=org.apache.log4j.patternlayout
LOG4J.APPENDER.CONSOLE.LAYOUT.CONVERSIONPATTERN=[%P][%D{YYYY-MM-DD Hh\:mm\:ss,sss}][%c{1}:%l]%m%n

Log4j.appender.onefile=org.apache.log4j.rollingfileappender 
log4j.appender.onefile.file=. /test.log
log4j.appender.onefile.maxfilesize=10mb
log4j.appender.onefile.threshold=all
Log4j.appender.onefile.layout=org.apache.log4j.patternlayout
LOG4J.APPENDER.ONEFILE.LAYOUT.CONVERSIONPATTERN=[%P][%D{YYYY-MM-DD hh\:mm\:ss,sss}] [%c{1}:%L]%m%n