Load log4j.properties from jar file in webapp

Having environment specific log4j.properties inside a jar file is hardly an ideal solution, but if you find yourself in a similar situation:

import java.net.URL;
import org.apache.log4j.PropertyConfigurator;
import javax.servlet.http.HttpServlet;

public class Log4jConfLoad extends HttpServlet {

  @Override
  public void init() {
    try {
      String prefix = "jar:file:" + getServletContext().getRealPath("/");
      String path = "WEB-INF/lib/the.jar!/" + System.getProperty("env") + "/log4j.properties";
      PropertyConfigurator.configure(new URL(prefix+path));
    catch (Exception ex) {
      //Because Servlet init can't be declared as throwing new exception.
      //Any thrown Exception here should show up in catalina.out (if Tomcat used)
      throw new RuntimeException(ex);
    }
  }
}

Also remember to add the servlet to web.xml with load-on-startup.