/* TODO runAs
    public void doStart()        throws Exception    {        _unavailable=0;        super.doStart();                if (!javax.servlet.Servlet.class            .isAssignableFrom(_class))        {            Exception ex = new IllegalStateException("Servlet "+_class+                                            " is not a javax.servlet.Servlet");            super.stop();            throw ex;        }                _config=new Config();                /* TODO runAs        if (_runAs!=null)            _realm=_httpHandler.getHttpContext().getRealm();        */                if (javax.servlet.SingleThreadModel.class            .isAssignableFrom(_class))            _servlets=new Stack();        if (_initOnStartup)        {            if (_servlet==null)                _servlet=(Servlet)newInstance();            try            {                initServlet(_servlet,_config);            }            catch(Throwable e)            {                _servlet=null;                _config=null;                if (e instanceof Exception)                    throw (Exception) e;                else if (e instanceof Error)                    throw (Error)e;                else                    throw new ServletException(e);            }                    }      }