public static long getLong(final String key, final String defaultValue) {
        return Long.parseLong(getProperty(key, defaultValue));
    }
get configs through system properties prior to default value

@author tsui
@version $Id: ConfigManager.java, v 0.1 2017-08-03 19:21 tsui Exp $
src/main/java/com/alipay/remoting/config/ConfigManager.java