When I want to forbidden some robort to acces my website,
I write somecode to extends the
org.apache.catalina.valves.RequestFilterValve  class.

package org.apache.catalina.valves;

import java.io.*;
import javax.servlet.*;

import org.apache.catalina.connector.*;

/**
 * <p>Title: Request Header Filter For Tomcat</p>
 * <p>Description:
 * eg: set follow coment in ${catalina.home}/conf/server.xml:
 * <Valve className="org.apache.catalina.valves.RequestHeaderValve"
header="User-Agent"
         deny="*httunit*"/>
 * then you can forbidden someone use httpunit to Access the Engine
,Host or Context
 * or:
 * <Valve className="org.apache.catalina.valves.RequestHeaderValve"
header="Referer"
         deny="*.mydomain.com, *localhost*"/>
 * then you can forbidden someone open the link from *.mydomain.com or
localhost
 * </p>
 * <p>Copyright: Apache License Version 2.0  </p>
 * <p>Company: lizongbo</p>
 * @author lizongbo @ gmail.com
 * @version 1.0
 */
public final class RequestHeaderValve
    extends RequestFilterValve {
  private String header = "";
  public void invoke(Request request, Response response) throws
IOException,
      ServletException {
    String headervalue = request.getRequest().getHeader(getHeader());
    headervalue = headervalue != null ? headervalue : "";
    process(headervalue, request, response);
  }

  public String getHeader() {
    return header;
  }

  public void setHeader(String header) {
    this.header = header;
  }