How to enable Logger.debug() in Log4j

Question

While trying to execute the following lines only the last two statements are displayed("Here is some ERROR" and "Here is some FATAL") and the first three statements are not displayed.I had just started to learn this topic, can anyone tell why is this happening?

    logger.debug("Here is some DEBUG");
    logger.info("Here is some INFO");
    logger.warn("Here is some WARN");
    logger.error("Here is some ERROR");
    logger.fatal("Here is some FATAL");

the log4j.property has

log4j.rootLogger=debug,stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=[%5p] %d{mm:ss}(%F:%M:%L)%n%m%n%n

Answer 1

Here's a quick one-line hack that I occasionally use to temporarily turn on debug logging in a JUnit test:

Logger.getRootLogger().setLevel(Level.DEBUG);

Answer 2

Put a file named log4j.xml into your classpath. Contents are e.g.

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

    <appender name="stdout" class="org.apache.log4j.ConsoleAppender">
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%d{ABSOLUTE} %5p %t %c{1}:%L - %m%n"/>
        </layout>
    </appender>

    <root>
        <level value="debug"/>
        <appender-ref ref="stdout"/>
    </root>

</log4j:configuration>

Answer 3

You probably have a log4j.properties file somewhere in the project. In that file you can configure which level of debug output you want. See this example:

log4j.rootLogger=info, console

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

log4j.logger.com.example=debug

The first line sets the log level for the root logger to "info", i.e. only info, warn, error and fatal will be printed to the console (which is the appender defined a little below that).

The last line sets the logger for com.example.* (if you get your loggers via LogFactory.getLogger(getClass())) will be at debug level, i.e. debug will also be printed.

Answer 4

If you are coming here because you are using Apache commons logging with log4j and log4j isn't working as you expect then check that you actually have a log4j.jar in your run-time classpath. That one had me puzzled for a little while. I have now configured the runner in my dev environment to include -Dlog4j.debug in the Java command line so I can always see that Log4j is being initialized correctly

Answer 5

I like to use a rolling file appender to write the logging info to a file. My log4j properties file typically looks something like this. I prefer this way since I like to make package specific logging in case I need varying degrees of logging for different packages. Only one package is mentioned in the example.

log4j.appender.RCS=org.apache.log4j.DailyRollingFileAppender
log4j.appender.RCS.File.DateFormat='.'yyyy-ww
#define output location
log4j.appender.RCS.File=C:temp/logs/MyService.log
#define the file layout
log4j.appender.RCS.layout=org.apache.log4j.PatternLayout
log4j.appender.RCS.layout.ConversionPattern=%d{yyyy-MM-dd hh:mm a} %5 %c{1}: Line#%L - %m%n
log4j.rootLogger=warn
#Define package specific logging
log4j.logger.MyService=debug, RCS

Answer 6

This is probably happening because your log4j configuration is set to ERROR. Look for a log4j.properties file with contents like the following:

log4j.rootLogger=ERROR, CONSOLE

# console logging
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Threshold=DEBUG
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d %-5p %-20.20t %-24c{1}: %m%n

The rootLogger is set to ERROR level here using a CONSOLE appender.

Note that some appenders like the console appender also have a Threshold property that can be used to overrule the rootLoggers level. You need to check both in this case.