首先加入log4j.properties文件。步骤：tomcat-->common-->classes.
具体文件内容：
log4j.rootLogger=info,Console,R
log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
#log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p %c – %m%n
log4j.appender.Console.layout.ConversionPattern=%d{yy-MM-dd HH:mm:ss} %5p %c{1}:%L – %m%n
log4j.appender.R=org.apache.log4j.DailyRollingFileAppender
log4j.appender.R.File=${catalina.home}/logs/tomcat.log
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d{yyyy.MM.dd HH:mm:ss} %5p %c{1}(%L):? %m%n
log4j.logger.org.apache=info, R
log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost]=DEBUG, R
log4j.logger.org.apache.catalina.core=info, R
log4j.logger.org.apache.catalina.session=info, R
其次加入 commons-logging-1.0.4.jar，log4j-1.2.15.jar两个包。步骤：tomcat-->common-->lib.
原文：http://www.cnblogs.com/hardwork/p/4061985.html