Log4j Logging Level in java

Question

Let's say I have the below line in log4j.properties

log4j.rootLogger=DEBUG,file
..
..

Does my java application capture all loggings with log.debug() alone ?

or

Does my java application capture all loggings with debug,info, warn,and error also

What do I need to do if I need only INFO and ERROR?

I agree with bradimus. Why are asking other people what is nicely documented, probably a zillion times? See for example: stackoverflow.com/questions/5817738/… — GhostCat
– GhostCat, Commented Aug 23, 2016 at 14:20
If rootLogger is set to DEBUG it will print out DEBUG, INFO, WARN, ERROR. If you want to filter for INFO and ERROR, only then you need to configure a filter in your appenders. See stackoverflow.com/documentation/java/2472/log4j-log4j2/19786/… — Fildor
– Fildor, Commented Aug 23, 2016 at 14:27
ok thanks, I am also going through Log4j docs as per previous comments — Surender Raja
– Surender Raja, Commented Aug 23, 2016 at 14:31

Arthur Noseda · Accepted Answer · 2016-08-23 15:42:13Z

The best course to really understand is to see for yourself.

LogLevelDemo.java

public class LogLevelDemo {

    private static final Logger LOG = Logger.getLogger(LogLevelDemo.class);

    public void log() {
        LOG.fatal("This is fatal.");
        LOG.error("This is error.");
        LOG.warn("This is warn.");
        LOG.info("This is info.");
        LOG.debug("This is debug.");
        LOG.trace("This is trace.");
    }

    public static void main(String[] args) {
        LogLevelDemo lld = new LogLevelDemo();
        lld.log();
    }

}

log4j.properties

log4j.rootLogger=INFO,A1
log4j.appender.A1=org.apache.log4j.ConsoleAppender

log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

And then switch the log4j.rootLogger level attribute to the level your want to test.

these settings print the following:

0    [main] FATAL demo.log4j.LogLevelDemo  - This is fatal.
0    [main] ERROR demo.log4j.LogLevelDemo  - This is error.
0    [main] WARN  demo.log4j.LogLevelDemo  - This is warn.
0    [main] INFO  demo.log4j.LogLevelDemo  - This is info.

Hence no debug or trace statements, and so on and so forth.

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