how to make log4j to write to the console as well

71
votes

Is there any way to tell to log4j to write its log to the file and to the console? thanks there are my properties:

log4j.rootLogger=DEBUG,console,R
log4j.rootLogger=INFO, FILE

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=%d{yyyy-MM-dd HH:mm:ss,SSS} %-5p - %m%n

log4j.appender.FILE=org.apache.log4j.RollingFileAppender
log4j.appender.FILE.File=log4j.log
log4j.appender.FILE.MaxFileSize=512KB
log4j.appender.FILE.MaxBackupIndex=3
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
log4j.appender.FILE.layout.conversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %-5p - %m%n
5
javaapachelogginglog4j
what does R mean? – Lei Yang

5 Answers

73
votes

Your root logger definition is a bit confused. See the log4j documentation.

This is a standard Java properties file, which means that lines are treated as key=value pairs. Your second log4j.rootLogger line is overwriting the first, which explains why you aren't seeing anything on the console appender.

You need to merge your two rootLogger definitions into one. It looks like you're trying to have DEBUG messages go to the console and INFO messages to the file. The root logger can only have one level, so you need to change your configuration so that the appenders have appropriate levels.

While I haven't verified that this is correct, I'd guess it'll look something like this:

log4j.rootLogger=DEBUG,console,file
log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.file=org.apache.log4j.RollingFileAppender

Note that you also have an error in casing - you have console lowercase in one place and in CAPS in another.

39
votes

Your log4j File should look something like below read comments.

# Define the types of logger and level of logging    
log4j.rootLogger = DEBUG,console, FILE

# Define the File appender    
log4j.appender.FILE=org.apache.log4j.FileAppender    

# Define Console Appender    
log4j.appender.console=org.apache.log4j.ConsoleAppender    

# Define the layout for console appender. If you do not 
# define it, you will get an error    
log4j.appender.console.layout=org.apache.log4j.PatternLayout

# Set the name of the file    
log4j.appender.FILE.File=log.out

# Set the immediate flush to true (default)    
log4j.appender.FILE.ImmediateFlush=true

# Set the threshold to debug mode    
log4j.appender.FILE.Threshold=debug

# Set the append to false, overwrite    
log4j.appender.FILE.Append=false

# Define the layout for file appender    
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout    
log4j.appender.FILE.layout.conversionPattern=%m%n
7
votes

This works well for console in debug mode

log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.Threshold=DEBUG
log4j.appender.console.Target=System.out
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.conversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %-5p - %m%n
0
votes

Write the root logger as below for logging on both console and FILE

log4j.rootLogger=ERROR,console,FILE

And write the respective definitions like Target, Layout, and ConversionPattern (MaxFileSize for file etc).

0
votes

Thats the exact usecase I was looking for my command line based tool. Wanted to show INFO on console but wanted to log more detailed info to log file. After various suggestion, finally go this solved by using 'log4j.appender.FILE.Threshold' Something like below.:

log4j.rootLogger=DEBUG,CONSOLE,FILE
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.FILE=org.apache.log4j.RollingFileAppender
log4j.appender.FILE.File=output/log.log
log4j.appender.CONSOLE.Threshold=INFO
log4j.appender.FILE.Threshold=DEBUG