private String prefix(String appName) {
        return appName == null ? StringUtils.EMPTY : "[" + appName + "]";
    }
Logger base on native slf4j

@author <a href="mailto:zhanggeng.zg@antfin.com">GengZhang</a>
core-impl/log/src/main/java/com/alipay/sofa/rpc/log/SLF4JLoggerImpl.java