//正常返回的JSON数据包
{
   "openid": "OPENID",
   "session_key": "SESSIONKEY"
   "expires_in": 2592000
}

//错误时返回JSON数据包(示例为Code无效)
{
  "errcode": 40029,
  "errmsg": "invalid code"
}

//@Param code 用户登录微信生成的code
//@Return OAuthResult 返回包含openid和session_key和expires_in的类
public OAuthResult getOAuthResultByCode(String code) {
    String path = "/sns/jscode2session";
    Map<String, Object> parameters = new HashMap<>();
    parameters.put("appid", WechatConstant.WECHAT_APP_ID);
    parameters.put("secret", WechatConstant.WECHAT_APP_SECRET);
    parameters.put("js_code", code);
    parameters.put("grant_type", "authorization_code");

    OAuthResult oAuthResult = messageSender.getMessageForObject(path, parameters, OAuthResult.class, false);
    if (oAuthResult.getOpenid() == null){
      throw new BusinessException(BusinessException.Code.OAUTH_PROCESS_ERROR, "OAuth异常，原因：" + oAuthResult.getErrmsg());
    }
    return oAuthResult;
  }