code: public void setJsonFactory(IJsonFactory jsonFactory) {
  		if (jsonFactory == null) {
  			throw new IllegalArgumentException("jsonFactory can not be null.");
  		}
  		JsonManager.me().setDefaultJsonFactory(jsonFactory);
  	}
docs: 设置 Json 转换工厂实现类，目前支持：JFinalJsonFactory(默认)、JacksonFactory、FastJsonFactory
  分别支持 JFinalJson、Jackson、FastJson