public class RedirectServletFilter implements javax.servlet.Filter {
  

  public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws ServletException, IOException {
    
    try {
      HttpServletRequest request = (HttpServletRequest) req;
      HttpServletResponse response = (HttpServletResponse) res;
      
      if( "/".equals( request.getPathInfo() ) ) {
        response.sendRedirect( response.encodeRedirectURL( "servlet_name" ) );
      } 
      else {
        chain.doFilter(request, response);
      }
    } catch (ClassCastException e) {
      throw new ServletException("non-HTTP request or response");
    }
    
  }

  public void init(FilterConfig filterConfig) {
  }

  public void destroy() {
  }
}

   <extension
         point="org.eclipse.equinox.http.registry.filters">
      <filter
            alias="/"
            class="org.example.RedirectServletFilter"
            load-on-startup="true">
      </filter>
   </extension>