Log4j getAppender从xml返回null

当我试图从XML中读取appender时，返回null

这是我的档案。xml

<appender name="FileInfoStatistics"   class="utils.monitorstatistics.CustonAppenderRollFile"> 
<param name="file" value="Statistics.log"/> 
<param name="MaxFileSize" value="100KB"/>
<layout class="utils.monitorstatistics.CustomAppenderStatistics"> 
    <param name="ConversionPattern" value="%-5p %c{1} - %m%n"/> 
</layout> 
</appender>

<logger name="utils.monitorstatistics" additivity="false">
<level value="INFO"/>

<appender-ref ref="FileInfoStatistics"/>
</logger>

getAppender返回空值

Logger mylogger = Logger.getLogger("utils.monitorstatistics");
Appender app = mylogger.getAppender("FileInfoStatistics");