帮忙看个tomcat启动的错误：严重: Error reading tld listeners java.lang.NullPointerException

信息: XML validation disabled
log4j:WARN No appenders could be found for logger (org.apache.catalina.startup.TldConfig).
log4j:WARN Please initialize the log4j system properly.
2009-3-5 11:20:52 org.apache.catalina.core.StandardContext start
严重: Error listenerStart
2009-3-5 11:20:52 org.apache.catalina.core.StandardContext start
严重: Context [/loa] startup failed due to previous errors
Stopping filters
Shutting down Log4J
2009-3-5 11:20:52 org.apache.catalina.core.StandardContext processTlds
严重: Error reading tld listeners java.lang.NullPointerException
java.lang.NullPointerException
at org.apache.log4j.Category.isEnabledFor(Category.java:749)
at org.apache.commons.logging.impl.Log4JLogger.isTraceEnabled(Log4JLogger.java:333)
at org.apache.catalina.startup.TldConfig.tldScanResourcePaths(TldConfig.java:581)
at org.apache.catalina.startup.TldConfig.execute(TldConfig.java:282)
at org.apache.catalina.core.StandardContext.processTlds(StandardContext.java:4278)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4115)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:759)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:739)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:524)
at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:608)
at org.apache.catalina.startup.HostConfig.deployDescriptors(HostConfig.java:535)
at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:470)
at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1122)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:310)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1021)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:718)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1013)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:442)
at org.apache.catalina.core.StandardService.start(StandardService.java:450)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:709)
at org.apache.catalina.startup.Catalina.start(Catalina.java:551)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:294)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:432)
2009-3-5 11:20:53 org.apache.catalina.core.StandardContext processTlds开始tomcat启动是没有问题的，但是我新加了一个类。在xml配置文件里配置了以后就出问题了。这是什么原因啊？用的struts框架和log4j的日志