Priority Levels of Logging statements in Log4j?

Priority Levels of Logging statements:

To insert logging statements in a java class we should assign some priority for those statements.

Log4j has given priority levels and respective methods but it is a programmer responsibility to apply an appropriate level for a statement.

The priority levels of a log4j are

1) ALL

2) TRACE

3) DEBUG

4) INFO

5) WARN

6) ERROR

7) FATAL

8) OFF

ALL<TRACE<DEBUG<INFO<WARN<ERROR<FATAL<OFF

->The standard priority levels used in a java application are…

     

1)DEBUG:

To indicate a control enter or exit from a method or class or module of a project

2)INFO:

To indicate some information like a server started or a connection is opened or an application is deployed or a connection is closed or server or services are closed

3)WARN:

To indicate some warning messages like a connection between client and server is lost or a socket is reached its limit etc.

4)ERROR:

To indicate some error message .Generally, we use this level in catch block of our code.

5)FATAL:

To indicate some un-recoverable error or problem. Generally, when a fatal error occurs then the application is aborted or terminated.

log4j.properties

log4j.rootLogger=DEBUG, A1

log4j.appender.A1=org.apache.log4j.FileAppender
log4j.appender.A1.file=mylog.txt

log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern= %m %n

•         log4j.rootLogger = DEBUG,A1 — > Here DEBUG means we are specifying the level from where log4j methods execution must start,  see mylog.txt file it showing all messages right.  But if we wrote log4j.rootLogger = WARN,A1 then it will prints the messages in l.warn(), l.error(), l.fatal() only  printed ,remaining logs ignore like  l.debug(), l.info() because of priority.

•         I have used FileAppender as my Appender, so if we want to change my appender to ConsoleAppender, i will open log4j.properties file and do the modifications,  so no need to touch our java classes, this is the main advantage of log4j.properties file.