在记录日志的时候，我们可能有这种需求，对于每个记录除了知道日志信息外，也要当前登录用户的信息。

可以这样解决：使用log4j的MDC

在web.xml加入 Filter：

<filter>

  <filter-name>set log4j MDC for log2userId</filter-name>

  <filter-class>UserFilter</filter-class>

  </filter>

  <filter-mapping>

  <filter-name>set log4j MDC for log2userId</filter-name>

  <url-pattern>

public class UserFilter implements Filter {

    

    private static final Logger logger = Logger.getLogger(UserFilter.class);

    private final static String DEFAULT_USERID="anonymous";

 

    public void doFilter(ServletRequest request, ServletResponse response,

            FilterChain chain) throws IOException, ServletException {

        HttpServletRequest req=(HttpServletRequest)request;

        HttpSession session= req.getSession();

        if (session==null){

            MDC.put("userId",DEFAULT_USERID);  

        }

        else{

            Customer customer=(Customer)session.getAttribute("customer");

            if (customer==null){

                MDC.put("userId",DEFAULT_USERID);

            }

            else

            {

                MDC.put("userId",customer.getLoginid());

            }

        }

        logger.info("test for MDC.");

        

        chain.doFilter(request,response);

    }

    public void init(FilterConfig fc) throws ServletException {

        

        // do nothing

        

    }

    public void destroy() {

//         do nothing

    }

}

在log4j.properties中加入新配置，示例使用jdbc存储

log4j.appender.db=org.apache.log4j.jdbc.JDBCAppender

#log4j.appender.db.BufferSize=100

log4j.appender.db.URL=jdbc:ulr

log4j.appender.db.driver=org.hsqldb.jdbcDriver

log4j.appender.db.user=sa

log4j.appender.db.password=

log4j.appender.db.sql=INSERT INTO LOG4J_MSG (LOGINID,PRIORITY,LOGDATE,CLASS,METHOD,MSG) VALUES('%X{userId}','%p','%d{yyyy-MM-dd HH:mm:ss}','%C','%M','%m')

%X{userId}：就是取出MDC的代码了