import com.foo.Bar;

 // Import log4j classes.
 import org.apache.log4j.Logger;
 import org.apache.log4j.BasicConfigurator;

 public class MyApp {

   // Define a static logger variable so that it references the
   // Logger instance named "MyApp".
   static Logger logger = Logger.getLogger(MyApp.class);

   public static void main(String[] args) {

     // Set up a simple configuration that logs on the console.
     BasicConfigurator.configure();

     logger.setLevel(Level.DEBUG); // optional if log4j.properties file not used
     // Possible levels: TRACE, DEBUG, INFO, WARN, ERROR, and FATAL

     logger.info("Entering application.");
     Bar bar = new Bar();
     bar.doIt();
     logger.info("Exiting application.");
   }
 }

private static Logger log = Logger.getLogger(<class name>.class);

-Dlog4j.configuration=file:<path to log.properties file>

 <!-- log info level into log.xml -->
 <appender name="XMLOut" class="org.apache.log4j.FileAppender"> 
        <param name="File" value="log.xml"/>  
        <param name="Threshold" value="info"/> 
        <layout class="org.apache.log4j.xml.XMLLayout"/>
    </appender> 

# HOW TO USE LOG4J WITHIN ECLIPSE IN 10 MINUTES
# by Daniel Gonzalez Gasull  gasull[at]gmail[dot]com
#
# 1) Download log4j http://logging.apache.org/site/binindex.cgi
# 2) Unpack the .zip file in your Java folder (In Windows it is usually 
# C:\Program Files\Java\)
# 3) In Eclipse: Window - Preferences... - Java - Build Path - User Libraries - 
# New - write "log4j" - OK - Add JARs... - navigate to find your log4j .jar you just
# unpacked in the Java Folder - OK 
# 4) right click on your project in the Package Explorer - New - Folder - 
# in "Folder name" write "log4j" - click Advanced - select "Link to a folder in the
# file system" - create a new folder "log4j" in your project folder in the file system
# 5) Place this file you are reading right now in in the folder you just created.  Name
# the file as log4j.properties
# 6) In Eclipse: Run - Run... - In the navigation bar on the left select either the 
# server, or the runnable class, or the JUnit test you want to log with log4j -
# select the Classpath tab - User Entries - Advanced... - Add folders - OK - select 
# the "log4j" folder you created in your project - OK   
# 7) Repeat step 6 for other servers, runnable classes or JUnit tests you want to log
# 8) Change in the following line the "org.example.foo.bar" with whatever you want.
log4j.category.org.example.foo.bar=DEBUG
# 9) Add the following import to the Java Class you want to log:
#	import org.apache.log4j.Logger;
# 10) Add this lines to the Java Class you want to log:
#	/**
#	 * Log4j logger
#	 */
#	static Logger log4j = Logger.getLogger("org.example.foo.bar");
# 11) Substitute in the code above "org.example.foo.bar" with whatever your wrote in
# in the step 8.
# 12) Add something like the following code in your Class whenever you want to log:
#	log4j.debug("WTF?");
# 13) Repeat steps 9, 10, 11 and 12 for every Java Class you want to log
# 14) Enjoy!


log4j.rootCategory=DEBUG, R, O

# Stdout
log4j.appender.O=org.apache.log4j.ConsoleAppender

# File
log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=log4j.log

# Control the maximum log file size
log4j.appender.R.MaxFileSize=100KB

# Archive log files (one backup file here)
log4j.appender.R.MaxBackupIndex=1

log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.O.layout=org.apache.log4j.PatternLayout

log4j.appender.R.layout.ConversionPattern=[%d{ISO8601}]%5p%6.6r[%t]%x - %C.%M(%F:%L) - %m%n
log4j.appender.O.layout.ConversionPattern=[%d{ISO8601}]%5p%6.6r[%t]%x - %C.%M(%F:%L) - %m%n

(new DOMConfigurator()).doConfigure(resourceManager().inputStreamForResourceNamed("log4j.xml", "app", null), LogManager.getLoggerRepository());