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
2
3 log4jfilter
4 org.fgq.study.log4j.Log4jFilter
5
6 sign
7 000010x
8
9
10
11 log4jfilter
12 /*
13
14
web.xml配置
doFilterInternal方法：
1 protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throwsServletException, 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
