在tomcat启动的时候，出现这个警告：
log4j:WARN No appenders could be found for logger (org.apache.commons.digester.Digester.sax).
log4j:WARN Please initialize the log4j system properly.
解决办法：
log4j.properties文件需要放到web-inf/class目录下面,在eclipse里面放到src目录下面，会自动拷贝到class目录下面去。
文件里面的内容如下即可：
log4j.rootLogger=WARN, Console
log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern=(%r ms) [%t] %-5p: %c#%M %x: %m%n
log4j.logger.com.genuitec.eclipse.sqlexplorer=DEBUG
log4j.logger.org.apache=WARN
log4j.logger.org.hibernate=WARN
有可能还需要配置web.xml
<context-param>
<param-name>log4jConfigLocation</param-name>
<param-value>classpath:log4j.properties</param-value>
</context-param>