private static Logger logger = Logger.getLogger(MyClass.class);
...
	logger.fatal("text");
	logger.error("text");
	logger.warn("text");
	logger.info("text");
	logger.debug("text");
	logger.info("text");
...
	if (logger.isTraceEnabled())
		logger.trace("lo: " + lo + " hi: " + hi + " min: " + min + " max: " + max + " rel: " + rel);
...
	if ((new File("log4j.properties")).canRead())
		PropertyConfigurator.configure("log4j.properties");

log4j.properties

log4j.rootLogger=TRACE, A1
log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout

# Print the date in ISO 8601 format
log4j.appender.A1.layout.ConversionPattern=%d [%t] %-5p %c - %m%n

log4j.logger.gui.MainFrame=INFO

… because it is easier than // System.out.println(...) all over the code

Since JDK 1.4 there is a logging framework inside the Java core packages.

AFAIK log4j provides more features and is at least as stable, so I keep using log4j.

Read more opinions http://www.google.at/search?q=log4j+java.util.logging

Commons Logging seems to be a compatibility layer so that a library can work with different logging implementations.

Whatever you do, don't break your program: If the program reads a log4.properties file from the file system, the file will likely get lost and users will be confronted with a FileNotFoundException and might not be able to run the program.

Here is a solution that works well for me:

1. a default log4j.properties file is located in the root directory of the classpath
   • if you work with Eclipse, this will be your ./src directory
   • if you create a jar-file, this will be the root directory of the jar-file
   • for the default settings use minimal logging (e.g., ConsoleAppender, WARN level)
2. a customized log4j.properties file is located in the working directory
   • if you work with Eclipse, this will be the project directory
3. in the main method check, whether log4j.properties exists in the working directory
   • if it exist, then load this file
   • if it does not exist, log4j will load the file from the classpath by default
4. if users want to override this behavior, they can
   • delete the log4j.properties from the working directory AND
   • specify the url of the configuration as a Java system property (e.g., -Dlog4j.configuration=file:/home/alex/log4j.properties)

• Short introduction to log4j by Ceki Gülcü, March 2002.
• API documentation