@WebServlet("/encoding")
public class EncodingServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        PrintWriter out = resp.getWriter();
        req.getRequestDispatcher("encoding.jsp").forward(req, resp);
    }
}

  /**
     * Returns a <code>PrintWriter</code> object that
     * can send character text to the client.
     * The <code>PrintWriter</code> uses the character
     * encoding returned by {@link #getCharacterEncoding}.
     * If the response's character encoding has not been
     * specified as described in <code>getCharacterEncoding</code>
     * (i.e., the method just returns the default value 
     * <code>ISO-8859-1</code>), <code>getWriter</code>
     * updates it to <code>ISO-8859-1</code>.
     * <p>Calling flush() on the <code>PrintWriter</code>
     * commits the response.
     * <p>Either this method or {@link #getOutputStream} may be called
     * to write the body, not both, except when {@link #reset}
     * has been called.
     * 
     * @return a <code>PrintWriter</code> object that 
     * can return character data to the client 
     *
     * @exception java.io.UnsupportedEncodingException
     * if the character encoding returned
     * by <code>getCharacterEncoding</code> cannot be used
     *
     * @exception IllegalStateException
     * if the <code>getOutputStream</code>
     * method has already been called for this response object
     *
     * @exception IOException
     * if an input or output exception occurred
     *
     * @see #getOutputStream
     * @see #setCharacterEncoding
     * @see #reset
     */

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        log(resp.getCharacterEncoding());              
        PrintWriter out = resp.getWriter();
        req.getRequestDispatcher("encoding.jsp").forward(req, resp);
    }

16:43:57,342 INFO  [io.undertow.servlet] (default task-11) EncodingServlet: ISO-8859-1

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        log(resp.getCharacterEncoding());
        PrintWriter out = resp.getWriter();
        req.getRequestDispatcher("encoding.jsp").forward(req, resp);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setCharacterEncoding("utf-8");
        log(resp.getCharacterEncoding());
        PrintWriter out = resp.getWriter();
        req.getRequestDispatcher("encoding.jsp").forward(req, resp);
    }

16:45:28,226 INFO  [io.undertow.servlet] (default task-21) EncodingServlet: utf-8

        req.getRequestDispatcher("xxx").include(req, resp);