Tomcat Error[SEVERE: Error listenerStart] on accessing web application with Spring/Log4j/Hibernate/Ant?

I can't access my web application deployed on tomcat via Ant. It is deployed fine, but, when I access it, browser gave me 404 error. The catalina log gave me the following exception. It previously worked. Did I missed any thing?

Aug 11, 2011 12:06:47 PM org.apache.catalina.startup.HostConfig deployWAR
INFO: Deploying web application archive customercare.war
log4j:WARN No appenders could be found for logger (org.apache.commons.digester.Digester).
log4j:WARN Please initialize the log4j system properly.
Aug 11, 2011 12:07:01 PM org.apache.catalina.core.StandardContext start
SEVERE: Error listenerStart
Aug 11, 2011 12:07:01 PM org.apache.catalina.core.StandardContext s开发者_JAVA百科tart
SEVERE: Context [/customercare] startup failed due to previous errors
Exception in thread "Timer-4" java.lang.NullPointerException
    at com.mchange.v2.log.log4j.Log4jMLog$Log4jMLogger.isLoggable(Log4jMLog.java:257)
    at com.mchange.v2.resourcepool.BasicResourcePool$CullTask.run(BasicResourcePool.java:1934)
    at java.util.TimerThread.mainLoop(Timer.java:512)
    at java.util.TimerThread.run(Timer.java:462)

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Your logger is not configured right:

The line that causes the error is in the inner class Log4jMLogger of the outer one Log4jMLog

The line that causes the error is: return logger.isEnabledFor( level(l) ); So your stack trace means that the variable logger is null.