1.先把把commons-logging.jar 和 log4j-xxx.jar 拷贝到 tomcat.home/common/lib/ 下.在 tomcat.home/common/classes/ 下建个 log4j.properties 就行了.这样所有输出信息可以由 log4j.properties 控制.
log4j.properties 文件:

# For JBoss: Avoid to setup Log4J outside $JBOSS_HOME/server/default/deploy/log4j.xml!
# For all other servers: Comment out the Log4J listener in web.xml to activate Log4J.
log4j.rootLogger=INFO, stdout, logfile

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - <%m>%n

log4j.appender.logfile=org.apache.log4j.RollingFileAppender
log4j.appender.logfile.File=/home/camry/work/logs/xxxx.log
log4j.appender.logfile.MaxFileSize=512KB
# Keep three backup files.
log4j.appender.logfile.MaxBackupIndex=3
# Pattern to output: date priority [category] - message
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=%d %p [%c] - %m%n
2.若你的 tomcat 中有好几个项目, 想不同项目日志写到不同位置去.可以在项目中创建个 Log4jInitServlet.class 来载入该项目的 log4j.properties.这时可以把 log4j.properties 放到 WEB-INF/ 下, 当然愿意放其他位置也可以.
代码如下:
WEB-INF/web.xml:
  <servlet> 
    <servlet-name>log4j-init</servlet-name> 
    <servlet-class> 
      com.xxx.xxxx.Log4jInitServlet 
    </servlet-class> 
    <init-param> 
      <param-name>log4j</param-name> 
      <!-- 这里标出了位置 --> 
      <param-value>/WEB-INF/log4j.properties</param-value> 
    </init-param> 
    <load-on-startup>1</load-on-startup> 
  </servlet> 
Log4jInitServlet.java :
package com.xxx.util; 
 
  import org.apache.log4j.PropertyConfigurator; 
 
  import javax.servlet.http.HttpServlet; 
  import javax.servlet.http.HttpServletRequest; 
  import javax.servlet.http.HttpServletResponse; 
 
  /** 
   * to-do init log4j. 
   */ 
  public class Log4jInitServlet extends HttpServlet { 
 
    /** 
     * initial. 
     */ 
    public void init() { 
      String prefix = getServletContext().getRealPath("/"); 
      // 读出上面标出的位置 
      String file = getInitParameter("log4j"); 
      PropertyConfigurator.configure(prefix + file); 
    } // END: init 
  } // END: Log4jInitServlet 
  ...