每次tomcat启动的时候都报这个错误，但是log4j已经配置好了，今天查了一下资料，原来是在tomcat/common/lib下多放了一个log4j的包的原因
原文：
Did you put a copy of log4j.jar back into common/lib? That error is coming from commons-logging finding Log4j and using it in preference to j2sdk1.4.x logging, but if Log4j doesn't, then, find its configuration, you will get that error. Note that commons-logging does a bunch of classloading trickery to find and load external logging packages. It is entirely possible that it might be using the context class loader to find Log4j, thus being able to bypass the normal Java2 classloader hierarchy (where only classloader higher in the hierarchy are visible). However, I just tested having log4j.jar in my WEB-INF/lib and not in common/lib and commons-logging in common/lib couldn't see it (and, therefore, didn't get the Log4j error), so it is most likely that you have log4j.jar in common/lib (or shared/lib) or some other place where commons-logging in Tomcat can see log4j.jar. Remove Log4j.jar and you won't see that error....or, I suppose, you could add log4j.xml or log4j.properties to common/classes and all would be well.
