通过slf4j/log4j的MDC/NDC 实现日志追踪

在分布式系统或者较为复杂的系统中，我们希望可以看到一个客户请求的处理过程所涉及到的所有子系统\模块的处理日志。

由于slf4j/log4j基本是日志记录的标准组件，所以slf4j/log4j成为了我的重点研究对象。

slf4j/log4j支持MDC，可以实现同一请求的日志追踪功能。

基本思路是：

实现自定义Filter，在接受到http请求时，计算eventID并存储在MDC中。如果涉及分布式多系统，那么向其他子系统发送请求时，需要携带此eventID。

源代码：https://github.com/athinboy/studyjava.git

其中：

response.setHeader("eventsign", eventsign);
很有用，返回的response中，将有httpheader：eventsign:000010x1489108079237

log4j日志格式配置为：

log4j.appender.stdout.layout.ConversionPattern=%d  %logger-%5p - %X{eventid} - %m%n

在web.xml中配置自定义filter:

1     protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
2
3         String eventsign;
4
5         if (request.getHeader("eventsign") == null || request.getHeader("eventsign").length() == 0) {
6             eventsign = this.sign + String.valueOf(new Date().getTime()); //计算eventID
7
8             logger.error("set eventid:" + eventsign);
9         } else {
10             eventsign = request.getHeader("eventsign");//从请求端获取eventsign
11             logger.error("get eventid from request:" + eventsign);
12
13         }
14
15         MDC.put("eventid",  eventsign);
16         response.setHeader("eventsign", eventsign);
17         filterChain.doFilter(request, response);
18
19
20     }

Log4jFilter-doFilterInternal

测试结果：

1、

Request URL:http://localhost:8084/spmvc/index.html
Request Method:GET
Status Code:304 Not Modified
Remote Address:[::1]:8084

Response Headers
Date:Fri, 10 Mar 2017 03:20:01 GMT
ETag:W/"660-1489115626000"
eventsign:000010x1489116001756

服务器端日志：
2017-03-10 11:20:01,756 org.fgq.study.log4j.Log4jFilter.doFilterInternal(Log4jFilter.java:59)ogger-ERROR - - set eventid:000010x1489116001756

2、
Request URL:http://localhost:8084/spmvc/mv/mvc/time?id=1
Request Method:GET
Status Code:200 OK
Remote Address:[::1]:8084

Response Headers
Content-Language:zh-CN
Content-Type:text/html;charset=utf-8
Date:Fri, 10 Mar 2017 03:21:02 GMT
Server:Apache-Coyote/1.1
Transfer-Encoding:chunked

Request Headers
Accept:*/*
Accept-Encoding:gzip, deflate, sdch, br
Accept-Language:zh-CN,zh;q=0.8
Connection:keep-alive
Cookie:eryewrhuewr
eventsign:eventsignOfQequest

服务器端日志：
2017-03-10 11:21:02,378 org.fgq.study.log4j.Log4jFilter.doFilterInternal(Log4jFilter.java:62)ogger-ERROR - - get eventid from request:eventsignOfQequest
2017-03-10 11:21:02,555 org.fgq.study.controller.TimeController.ShowTime(TimeController.java:34)ogger- WARN - 000010xeventsignOfQequest - get eventid:eventsignOfQequest, send request to other sub system ,and with the eventid!

返回内容：the eventsign is : eventsignOfQequest

参考： https://logback.qos.ch/manual/mdc.html