code: public static SnsToken oauth2RefreshToken(String appid,String refresh_token){
  		HttpUriRequest httpUriRequest = RequestBuilder.post()
  				.setUri(BASE_URI + "/sns/oauth2/refresh_token")
  				.addParameter("appid", appid)
  				.addParameter("refresh_token", refresh_token)
  				.addParameter("grant_type", "refresh_token")
  				.build();
  		return LocalHttpClient.executeJsonResult(httpUriRequest,SnsToken.class);
  	}
docs: 刷新access_token
  @param appid appid
  @param refresh_token refresh_token
  @return SnsToken