java - 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