Using Log4J in Web Application

Create a log4j.properties in your /classes folder - because only /classes and /lib folders will be in Tomcat ClassPath, the convention is to put all .properties files in /classes

Here is what my log4j.properties looks like:

  log4j.rootLogger=DEBUG, RollFileAppender   
     
  log4j.appender.RollFileAppender=org.apache.log4j.RollingFileAppender   
  log4j.appender.RollFileAppender.File=${catalina.home}/logs/HelloWorld.log  
  log4j.appender.RollFileAppender.layout=org.apache.log4j.PatternLayout   
  log4j.appender.RollFileAppender.layout.ConversionPattern=%p %d %C %L %n %m %n  

Remember to specify a log4j dependency in your ivy.xml:

 <ivy-module version="2.0">  
   <info organisation="org.confucius" module="helloworld"/>  
   <dependencies>  
     <dependency org="javax.servlet" name="servlet-api" rev="2.5"/>  
         <dependency org="log4j" name="log4j" rev="1.2.16"/>   
   </dependencies>  
 </ivy-module>  

Run the Ant:resolve target to download log4j.jar if necessary.

Remember to add log4j.jar to Eclipse->Project->Properties->JAVA Build Path->Libraries

Update your HelloWorld.java to use log4j:

  package org.confucius;   
     
  import java.io.IOException;   
  import javax.servlet.ServletException;   
  import javax.servlet.http.HttpServlet;   
  import javax.servlet.http.HttpServletRequest;   
  import javax.servlet.http.HttpServletResponse;   
  import org.apache.log4j.PropertyConfigurator;   
  import org.apache.log4j.Logger;     
     
  public class HelloWorld extends HttpServlet{   
    public void doGet (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException   
    {   
         PropertyConfigurator.configure("log4j.properties");   
         Logger logger = Logger.getLogger(HelloWorld.class);        
         logger.debug("Received age check request");   
   
         int year = Integer.parseInt(request.getParameter("year"));  
         if (year > 1995)  
              response.getWriter().println("You are underage!");  
         else  
              response.getWriter().println("You may enter!");  
    }   
  }   

Now if you build and redeploy HelloWorld.war, and do an age check, you will see a HelloWorld.log file in your tomcat_home/logs folder.