What does threshold mean in Log4J?

Question

I have a log4j properties something like below. Everything that is logged in TextProcessor.log is something above WARN level. I don't understand the threshold that is set here to debug. Can someone explain what the threshold does?

log4j.logger.TextProcessor=warn,TextProcessor   log4j.appender.TextProcessor=org.apache.log4j.RollingFileAppender log4j.appender.TextProcessor.File=C:/project/logs/TextProcessor.log log4j.appender.TextProcessor.MaxFileSize=10MB log4j.appender.TextProcessor.MaxBackupIndex=10 log4j.appender.TextProcessor.Threshold=debug log4j.appender.TextProcessor.layout=org.apache.log4j.PatternLayout log4j.appender.TextProcessor.layout.ConversionPattern=[%d] [%5p] (%F:%L) - %m%n 

Answer 1

You have two things here : a logger, and an appender. Unfortunately, you chose the same name for both, which doesn't make it very clear.

The logger's minimum level is set to warn, which means everything you log with this logger which doesn't have at least the warn level will be ignored.

Once a message is accepted by the logger, it's sent to one or several appenders (to a file, to the console, to a mail server, etc.). Each of these appenders may define a threshold. You could for example limit the messages in the console to errors, but accept warn messages in the log file.

Answer 2

Threshold is second filter for messages to be logged

e.g.:

 log4j.logger.TextProcessor=Debug,TextProcessor , InfoLogger  .  .  .  log4j.appender.TextProcessor.Threshold=Error 

if Logger is set at level DEBUG and appender Threshold is set at Error then with the appender TextProcessor only Error and higher severity messages would be logged.

Use of Threshold is ,you can define different appender with different threshold levels ,for e.g in above mentioned example you can also have InfoLogger with Info level messages logging enabled

 log4j.logger.TextProcessor=Debug,TextProcessor , InfoLogger  .  .  .  log4j.appender.InfoLogger.Threshold=INFO 

To understand levels , There are below levels of logging in log4j:

FATAL: shows messages at a FATAL level only   ERROR: Shows messages classified as ERROR and FATAL   WARNING: Shows messages classified as WARNING, ERROR, and FATAL   INFO: Shows messages classified as INFO, WARNING, ERROR, and FATAL   DEBUG: Shows messages classified as DEBUG, INFO, WARNING, ERROR, and FATAL   TRACE : Shows messages classified as TRACE,DEBUG, INFO, WARNING, ERROR, and FATAL ALL : Shows messages classified as TRACE,DEBUG, INFO, WARNING, ERROR, and FATAL  OFF : No log messages display 

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