1.demo

                returnJson(servletResponse, JSON.toJSONString(R.error(40027, "登录信息已失效,请重新登录")));
                return;

    private void returnJson(ServletResponse response, String json) {
        PrintWriter writer = null;
        response.setCharacterEncoding("UTF-8");
        response.setContentType("application/json; charset=utf-8");
        try {
            writer = response.getWriter();
            writer.print(json);

        } catch (IOException e) {
            log.error("response error", e);
        } finally {
            if (writer != null)
                writer.close();
        }
    }

2.效果

3.文章参考链接
a. https://blog.csdn.net/qq_37164847/article/details/89233349