servlet lifecycle interceptor methods ignored when declared in web.xml

  <post-construct>
    <lifecycle-callback-class>test.TestServlet</lifecycle-callback-class>
    <lifecycle-callback-method>ps</lifecycle-callback-method>
  </post-construct>
  <pre-destroy>
    <lifecycle-callback-class>test.TestServlet</lifecycle-callback-class>
    <lifecycle-callback-method>pd</lifecycle-callback-method>
  </pre-destroy>

    private void ps() {
        System.out.println("in post-construct declared in web.xml of " + this);
    }

    private void pd() {
        System.out.println("in pre-destroy declared in web.xml of " + this);
    }