apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/RetryableRestTemplate.java/RetryableRestTemplate/getAdminServiceAccessToken
class RetryableRestTemplate:  private String getAdminServiceAccessToken(Env env) {
    String accessTokens = portalConfig.getAdminServiceAccessTokens();

    if (Strings.isNullOrEmpty(accessTokens)) {
      return null;
    }

    if (!accessTokens.equals(lastAdminServiceAccessTokens)) {
      synchronized (this) {
        adminServiceAccessTokenMap = parseAdminServiceAccessTokens(accessTokens);
        lastAdminServiceAccessTokens = accessTokens;
      }
    }

    return adminServiceAccessTokenMap.get(env);
  }