java判断是不是微信客户端

        String ua =  request.getHeader("user-agent").toLowerCase();  
        if (ua.indexOf("micromessenger") > 0 && fileName.equalsIgnoreCase("iReadyInsights.apk")) {
            response.setHeader("Access-Control-Allow-Origin", "*");        
            response.setStatus(HttpStatus.UNAUTHORIZED.value());
            response.setContentType("application/json;charset=UTF-8");
            response.getWriter().write("请使用浏览器扫描二维码，进行安装包下载");
        }