Question

The task in my software involves several steps where each step may or may not execute in different threads. Each step has some log and I use log4j as logging service.

A headache problem is it’s hard to associate logs printed by different threads to the task they belongs to. In single thread mode, the thread name is a good indicator, but it doesn’t work in multiple threads mode. I don’t want to pass a task indicator through threads as it’s annoying and will burden programmer.

I wonder anybody faced the same problem and had a good solution? thank you.

Answer 1

Look for log4j’s documentation on MDC (Mapped Diagnostic Context) and NDC (Nested Diagnostic Context). Below is the excerpt from this article

Nested Diagnostic Context (NDC) and Mapped Diagnostic Context (MDC)
help in situations where one application is involved in simultaneously
serving multiple clients, and you are interested in separating or
distingushing log content from each of these multiple clients. A Web
application is a really good example of such a situation.

So how do we separate or distinguish content from multiple clients? By
marking each log statement with client-specific information. This, in
a typical Web application, could include, among other things, the
client’s IP address, which is readily available to the servlet
container. So, in NDC, you push this information on a stack when
entering a context, and pop it when leaving that context. log4j uses
this context-specific information when writing to the appender, if in
your associated layout, you use the %x conversion pattern.