log4j:WARN No appenders could be found for logger

[red phoenix]

I have some file like follows:
C:\tomcat5\webapps\ROOT\WEB-INF\web.xml
C:\tomcat5\webapps\ROOT\WEB-INF\conf\log4j.properties
C:\tomcat5\webapps\ROOT\WEB-INF\classes\test\LogServlet.class
C:\tomcat5\webapps\ROOT\WEB-INF\classes\abc\test.class

and I use servlet to initial log4j,like follows:

/*LogServlet.java*/
package test;
import javax.servlet.*;
import javax.servlet.http.*;
import org.apache.log4j.PropertyConfigurator;
public class LogServlet extends HttpServlet{
  public void init() throws ServletException {
        String prefix = getServletContext().getRealPath("/");
        String file =
getServletConfig().getInitParameter("log4j-config-file");
        if(file != null)
            PropertyConfigurator.configure(prefix + file);
   }
   public void doPost(HttpServletRequest request, HttpServletResponse
response)  throws ServletException, IOException{}
}

/*web.xml*/
.......
<servlet>
   <display-name>LogServlet</display-name>
  <servlet-name>LogServlet</servlet-name>
  <servlet-class>
   test.LogServlet
  </servlet-class>
  <init-param>
   <param-name>log4j-config-file</param-name>
   <param-value>
    /WEB-INF/conf/log4j.properties
   </param-value>
  </init-param>
  <load-on-startup>1</load-on-startup>
 </servlet>

/*log4j.properties*/
log4j.logger.A1=INFO, A1
log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%m%n

I find LogServlet execute successful,and then I write a class to write
log,like follows:

package abc;
import org.apache.log4j.Logger;
public class test{
 private static Logger log;
 public static void main(String args[]){
   Logger log=Logger.getLogger("A1");
  log.error("test");
 }

When I run test.class,I got error:

log4j:WARN No appenders could be found for logger (A1).
log4j:WARN Please initialize the log4j system properly.

Why raise above error? I am puzzled with it.
Thanks in advance.