code: @Override
      protected final void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
          if (!support.isLegal(request)) {
              return;
          }
          //设置响应编码格式
          response.setCharacterEncoding("UTF-8");
          String resp = support.processRequest(request);
          PrintWriter pw = response.getWriter();
          pw.write(resp);
          pw.flush();
          pw.close();
      }
docs: 重写servlet中的post方法，用于接收微信服务器发来的消息，置为final方法，用户已经无需重写这个方法啦
  
  @param request  http请求对象
  @param response http响应对象
  @throws ServletException servlet异常
  @throws IOException      IO异常