Respond encoding of Google App Engine(can not change response encoding)

public class FeedUpdaterServlet extends HttpServlet {

public void doGet(HttpServletRequest req, HttpServletResponse resp)

        throws IOException {

    PrintWriter out = resp.getWriter();

    req.setCharacterEncoding("utf-8");

    resp.setLocale(Locale.TAIWAN);

    resp.setContentType("text/html; charset=utf-8");

    resp.setCharacterEncoding("utf-8");

    resp.getWriter().println("Hello, world!!@!");

            out.println("我是人");  //some chinese character

    out.println(resp.getCharacterEncoding());

    out.flush();

    out.close();

  }



}

web xml

<locale-encoding-mapping-list>

        <locale-encoding-mapping>

            <locale>zh_TW</locale>

            <encoding>utf-8</encoding>

        </locale-encoding-mapping>

    </locale-encoding-mapping-list>

Output: Hello, world!!@! ??? ISO-8859-1

It seems that the encoding of the respond can not be changed, what is happening???