3.6. Using your own log4j.xml file - Log4j RepositorySelector

Another way to achieve this is to write a custom RepositorySelector that changes how the LogManager gets a logger. Using this technique, Logger.getLogger() will return a different logger based on the context class loader. Each context class loader has its own configuration set up with its own log4j.xml file. 
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package org.jboss.repositoryselectorexample;

import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.xml.parsers.DocumentBuilderFactory;
import org.apache.log4j.Hierarchy;
import org.apache.log4j.Level;
import org.apache.log4j.LogManager;
import org.apache.log4j.spi.LoggerRepository;
import org.apache.log4j.spi.RepositorySelector;
import org.apache.log4j.spi.RootCategory;
import org.apache.log4j.xml.DOMConfigurator;
import org.w3c.dom.Document;

/**
 * This RepositorySelector is for use with web applications.  
 * It assumes that your log4j.xml file is in the WEB-INF directory.
 * @author  Stan Silvert
 */
public class MyRepositorySelector implements RepositorySelector
{
   private static boolean initialized = false;

   // This object is used for the guard because it doesn't get
   // recycled when the application is redeployed.
   private static Object guard = LogManager.getRootLogger();
   
   private static Map repositories = new HashMap();
   private static LoggerRepository defaultRepository;

   /**
    * Register your web-app with this repository selector.
    */
   public static synchronized void init(ServletConfig config) 
        throws ServletException {
      if( !initialized ) // set the global RepositorySelector
      {
         defaultRepository = LogManager.getLoggerRepository();
         RepositorySelector theSelector = new MyRepositorySelector();
         LogManager.setRepositorySelector(theSelector, guard);
         initialized = true;
      }
      
      Hierarchy hierarchy = new Hierarchy(new
                                RootCategory(Level.DEBUG));
      loadLog4JConfig(config, hierarchy);
      ClassLoader loader = 
           Thread.currentThread().getContextClassLoader();
      repositories.put(loader, hierarchy);
   }

   // load log4j.xml from WEB-INF
   private static void loadLog4JConfig(ServletConfig config, 
                                       Hierarchy hierarchy) 
                                            throws ServletException {
        try {
            String log4jFile = "/WEB-INF/log4j.xml";
            InputStream log4JConfig = 
                
            config.getServletContext().getResourceAsStream(log4jFile);
            Document doc = DocumentBuilderFactory.newInstance()
                                                 .newDocumentBuilder()
                                                 .parse(log4JConfig);
            DOMConfigurator conf = new DOMConfigurator();
            conf.doConfigure(doc.getDocumentElement(), hierarchy);
        } catch (Exception e) {
            throw new ServletException(e);
        }
    }

   private MyRepositorySelector() {
   }

   public LoggerRepository getLoggerRepository() {
      ClassLoader loader = 
             Thread.currentThread().getContextClassLoader();
      LoggerRepository repository = 
            (LoggerRepository)repositories.get(loader);
      
      if (repository == null) {
          return defaultRepository;
      } else {
          return repository;
      }
   }
}