由伺服器（通過<code>service</code>方法）呼叫，以允許servlet處理TRACE請求。TRACE將隨TRACE請求一起傳送的報頭返回給客戶端，以便用於除錯。不需要重寫此方法。

 原始碼：

 /**
     * Called by the server (via the <code>service</code> method)
     * to allow a servlet to handle a TRACE request.
     *
     * A TRACE returns the headers sent with the TRACE
     * request to the client, so that they can be used in
     * debugging. There's no need to override this method.
     *
     * @param req   the {@link HttpServletRequest} object that
     *                  contains the request the client made of
     *                  the servlet
     *
     * @param resp  the {@link HttpServletResponse} object that
     *                  contains the response the servlet returns
     *                  to the client
     *
     * @exception IOException   if an input or output error occurs
     *                              while the servlet is handling the
     *                              TRACE request
     *
     * @exception ServletException  if the request for the
     *                                  TRACE cannot be handled
     */
    protected void doTrace(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {

        int responseLength;

        String CRLF = "\r\n";
        StringBuilder buffer = new StringBuilder("TRACE ").append(req.getRequestURI())
            .append(" ").append(req.getProtocol());

        Enumeration<String> reqHeaderEnum = req.getHeaderNames();

        while( reqHeaderEnum.hasMoreElements() ) {
            String headerName = reqHeaderEnum.nextElement();
            buffer.append(CRLF).append(headerName).append(": ")
                .append(req.getHeader(headerName));
        }

        buffer.append(CRLF);

        responseLength = buffer.length();

        resp.setContentType("message/http");
        resp.setContentLength(responseLength);
        ServletOutputStream out = resp.getOutputStream();
        out.print(buffer.toString());
        out.close();
        return;
    }
 

主要用於測試！