What is MDC context?

A Mapped Diagnostic Context, or MDC in short, is an instrument for distinguishing interleaved log output from different sources. Log output is typically interleaved when a server handles multiple clients near-simultaneously.

What is MDC class in SLF4J?

public class MDC extends Object. This class hides and serves as a substitute for the underlying logging system’s MDC implementation. If the underlying logging system offers MDC functionality, then SLF4J’s MDC, i.e. this class, will delegate to the underlying system’s MDC.

What is context based logging?

Contextual logging is an approach that encourages not just adding additional useful data to log events, but also sharing that data across related events. With contextual logging, data tokens are added to and removed from log events over the course of the application’s runtime.

How can the MDC context be used in the reactive spring applications?

We can use this technique to include session id, request id or actually any request specific property to each log message outputted during the execution of that specific request. The standard way of using the MDC is to set a context value bounded to a specific key.

What is MDC used for?

MDC in Log4j allows us to fill a map-like structure with pieces of information that are accessible to the appender when the log message is actually written. The MDC structure is internally attached to the executing thread in the same way a ThreadLocal variable would be.

What is thread context Log4j?

The ThreadContext allows applications to store information either in a Map or a Stack. The MDC is managed on a per thread basis. To enable automatic inheritance of copies of the MDC to newly created threads, enable the “isThreadContextMapInheritable” Log4j system property.

What is SLF4J vs Log4j?

Unlike log4j, SLF4J (Simple Logging Facade for Java) is not an implementation of logging framework, it is an abstraction for all those logging frameworks in Java similar to log4J. Therefore, you cannot compare both. However, it is always difficult to prefer one between the two.

Is SLF4J MDC thread-safe?

BTW, MDC is thread-safe. No worrying for concurrency. In multi-thread environment, if the child is create with the basic Thread + Runnable way, the child thread will automatically inherit parent’s MDC.

Does MDC use ThreadLocal?

Internally, MDC uses ThreadLocal and it has some predefined functionalities like adding a prefix to every log.

Is SLF4J logger thread-safe?

Logger is thread-safe (search for “multi-thread safe”)