code: public void removeVirtualHost(String hostname)
      {
          // Note that null hosts are also added.
          if (_vhosts.remove(hostname))
          {
              _contextName=null;
              if (_httpServer!=null)
              {
                  _httpServer.removeMapping(hostname,this);
                  if (_vhosts.size()==0)
                      _httpServer.addMapping(null,this);
              }
              _vhostsArray=null;
          }
      }
docs: remove a virtual host alias to this context.
  @see #setVirtualHosts
  @param hostname A hostname. A null host name means any hostname is
  acceptable. Host names may String representation of IP addresses.