How to initialize log4j properly?

Question

After adding log4j to my application I get the following output every time I execute my application:

log4j:WARN No appenders could be found for logger (slideselec         


        

Answer 1

Find a log4j.properties or log4j.xml online that has a root appender, and put it on your classpath.

### direct log messages to stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.SimpleLayout
log4j.rootLogger=debug, stdout

will log to the console. I prefer logging to a file so you can investigate afterwards.

log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.maxFileSize=100KB
log4j.appender.file.maxBackupIndex=5
log4j.appender.file.File=test.log
log4j.appender.file.threshold=debug
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n
log4j.rootLogger=debug,file

although for verbose logging applications 100KB usually needs to be increased to 1MB or 10MB, especially for debug.

Personally I set up multiple loggers, and set the root logger to warn or error level instead of debug.