2、在入口类的静态区初始化log4j

 static {
  PropertyConfigurator.configure(
   YesFTPClientFrame.class.getResource("log4j.properties"));
 }

3、在每一个需要log的地方都初始化一个私有静态的变量

 protected final Log logger = LogFactory.getLog(XX类.class);

4、使用log4j提供的方法

logger.info(”hello”);

5、用log4j输出异常的堆栈信息

logger.error("oops, got an exception: ", e); 


2007/09/18 增补

开发Tomcat等web程序时,应将log4j.properties放在Webapp的根目录下,然后用一个自启动Servlet指定设置log4j配置文件位置
如下:
org.apache.log4j.PropertyConfigurator.configure(realPath + "log4j.properties");

自启动类代码如下:

package com.sitinspring.projectpusher.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.sitinspring.projectpusher.util.CommonUtil;

/**
 * 初始化配置
 * @author Administrator
 *
 */
public class InitServlet extends HttpServlet {
 private static final long serialVersionUID = -7444606086930580188L;

 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, java.io.IOException {
 }

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, java.io.IOException {
  doPost(request, response);
 }

 public void init() throws ServletException {
  // 取得实际物理地址
  ServletContext sct = getServletContext();  
  String realPath=sct.getRealPath("/");
  
  // 设置log4j配置文件位置
  org.apache.log4j.PropertyConfigurator.configure(realPath + "log4j.properties");
  
  // 设置DB4O的数据文件实际位置
  CommonUtil.setDatafilePath(realPath);
 }
}

自启动类配置如下:
 <servlet>
  <servlet-name>InitServlet</servlet-name>
  <servlet-class>com.sitinspring.projectpusher.servlet.InitServlet</servlet-class>
  <load-on-startup>0</load-on-startup>
 </servlet>