java - Why do I get a duplicate Id in my MDC SLF4J for two requests? -

i have web application. application deployed tomcat. write servlet filter put data in mdc class @ slf4j following code:

mdc.put("id", uuid.randomuuid().tostring();

when run application second or third request duplicate uuid. scenario serial , isn't concurrent. think there exists thread pool thread context don't clear.

use structure guarantee id removed:

try {     mdc.put("id", uuid.randomuuid().tostring());      // rest of code } {     mdc.remove("id"); } 

(no catch block necessary). guarantee id key removed transaction.

also, of course tomcat uses thread pool, how manages requests when concurrent. further reading: https://tomcat.apache.org/tomcat-6.0-doc/config/executor.html