我已经获取到微信客户端返回的code，但是通过https://api.weixin.qq.com/sns/oauth2/access_toke网址没有获取到openid，网址无效果
解决方案
1.登录公众账号设置OAuth2.0
2.设置菜单按钮URL为OAuth链接
3.页面后台获取:
public String getopenId() { HttpServletRequest request = ServletActionContext.getRequest(); HttpServletResponse response = ServletActionContext.getResponse(); response.setContentType("text/html"); String code = request.getParameter("code"); String urlstr = "https://api.weixin.qq.com/sns/oauth2/access_token?appid=<appId>&secret=<secret>&code=" + code + "&grant_type=authorization_code"; JSONObject json; try { json = JSONObject.fromObject(HTTPTools.postToGetJson(urlstr)); openId = json.getString("openid"); } catch (Exception e) { // e.printStackTrace(); return ""; } return openId;}