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How to implement Client Specfic information in Log 4j

Posted on 2009-04-07
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Last Modified: 2012-05-06
Hi all,
         We have web application which is using Log4j for logging . But there is no client specific information in each statement  of log file. But we want to implememnt a client specific information in our logging system. Could you please tell me how to implement the NDC or any others on Log4j.
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Question by:balatrue
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by:tbsgadi
ID: 24087755
Have a look at the following:

http://wiki.apache.org/logging-log4j/NDCvsMDC

Gary
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Jim Cakalic earned 500 total points
ID: 24088366
I usually use the MDC to do this. Basically you've got to figure out somewhere in your application call path to add the information to the MDC and then where to remove it. MDC is essentially a ThreadLocal Map. Each thread of execution in the JVM will have its own Map of values. The problem is, if this is a web application then Servlet threads get reused. If you put data in the MDC and don't clear it at some point then when that thread is reused there will be stale values there. Again, if this is a web application, and you know the values to put into the MDC fairly early on, then you might consider implementing a Filter that does this for you. I do this a lot when I want to add SessionID the log.

So that's the hard part. Where do you put and clear the MDC. The easy part is, in your Appender's PatternLayout specification, add something like the following to the string: %X{mdcKey} where mdcKey is the key name of the value as you added it to the MDC. An example ... if you do this in your code:
    MDC.put("ClientID", clientID);

Then your pattern specification might look like this:
    [%t] %-5p %c %X{ClientID} - %m%n

Regards,
Jim
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