access_token的值的获取在后端进行，参考代码如下：

    private static final String getAccessTokenUrl = "https://api.weixin.qq.com/cgi-bin/token";
/**
     * 从url获取数据库获取access_token
     * @return
     */
    public String getAccessToken(){
        List<AccessTokenDto> accessTokenList = accessTokenService.queryAll(new AccessTokenQueryCriteria());
        if (accessTokenList.size() > 0){
            //过期的话刷新 ,保持时间是2个小时，7200秒
            if ((System.currentTimeMillis() - accessTokenList.get(0).getLastAccessTime().getTime())/1000 >= 7200){
                JSONObject jsonObject = getAccessTokenByUrl();
                String token = jsonObject.getString("access_token");
                Long expiresIn = jsonObject.getLong("expires_in");
                AccessToken accessToken = new AccessToken();
                accessToken.setAccessToken(token);
                accessToken.setExpiresIn(expiresIn);