Logging error to stderr and debug, info to stdout with log4j

Question

I want to add logging to an application I am developing, using apache log4j. At this point I want to redirect all log messages for level INFO and lower (TRACE, DEBUG) to stdout and all other log messages from WARN and above (ERROR, FATAL) to stderr. For example:

... logger.info("Processing at some point"); // must be written to stdout logger.debug("Point x was processed"); // must be written to stdout logger.warn("Incorrect point config"); // must be written only to stderr logger.error("Exception occurred at point x"); // must be written only to stderr 

So what should be my log4j.properties file? Here how it looks at this momment:

log4j.rootLogger=DEBUG, stdout, stderr  # configure stdout # set the conversion pattern of stdout # Print the date in ISO 8601 format log4j.appender.stdout = org.apache.log4j.ConsoleAppender log4j.appender.stdout.Threshold = DEBUG log4j.appender.stdout.Target   = System.out log4j.appender.stdout.layout = org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern = %-5p %d [%t][%F:%L] : %m%n  # configure stderr # set the conversion pattern of stdout # Print the date in ISO 8601 format log4j.appender.stderr = org.apache.log4j.ConsoleAppender log4j.appender.stderr.Threshold = WARN log4j.appender.stderr.Target   = System.err log4j.appender.stderr.layout = org.apache.log4j.PatternLayout log4j.appender.stderr.layout.ConversionPattern = %-5p %d [%t][%F:%L] : %m%n 

The problem with the above configuration is that the logger.error() ... is printed at stdout too.

Answer 1

Solved below also in properties file format. The trick was to get the filter definition right. Log4j properties info here

The original attempt, modified to filter WARN & ERROR:

log4j.rootLogger=TRACE, stdout, stderr  # configure stdout # set the conversion pattern of stdout # Print the date in ISO 8601 format log4j.appender.stdout = org.apache.log4j.ConsoleAppender log4j.appender.stdout.Threshold = TRACE log4j.appender.stdout.Target   = System.out log4j.appender.stdout.layout = org.apache.log4j.PatternLayout log4j.appender.stdout.layout.ConversionPattern = %-5p %d [%t][%F:%L] : %m%n log4j.appender.stdout.filter.filter1=org.apache.log4j.varia.LevelRangeFilter log4j.appender.stdout.filter.filter1.levelMin=TRACE log4j.appender.stdout.filter.filter1.levelMax=INFO  # configure stderr # set the conversion pattern of stdout # Print the date in ISO 8601 format log4j.appender.stderr = org.apache.log4j.ConsoleAppender log4j.appender.stderr.Threshold = WARN log4j.appender.stderr.Target   = System.err log4j.appender.stderr.layout = org.apache.log4j.PatternLayout log4j.appender.stderr.layout.ConversionPattern = %-5p %d [%t][%F:%L] : %m%n