![]() ![]() ![]() So i have added a hard coded value as below. This is a just sample demonstration of how to add the values to the MDC (Mapped Diagnostic Context) store. ![]() This will guarantee that MDC is properly populated with relevant data before any request reach its designated endpoint. The Servlet Filter will be the excellent centralized place to configure the MDC data store. Therefore we need to make sure that MDC is properly initialized and populated with related data before the request reach the targeted endpoint. In order to achieve this, we can use Servlet Filters. All application related log entries are added inside each Restful endpoint. If you look at the source code of this article, you may notice that this application is a Restful web api. Therefore we need to make sure that MDC (Mapped Diagnostic Context) is populated with related entries before generating the log entries. The logging framework may generate the log entries by adding the data/information stored in the MDC. MDC is a key value pair store (similar to java Map) and the stored values are used to enhance the log entries ( add meaningful information to log entries). all of them are mixed up.Īs we discuss above, the solution is to enhance the log entries by adding meaningful information with MDC.Įnhance the logging with MDC (Mapped Diagnostic Context) Since all the log entries are identical and no distinguishable information it is impossible to say which log entry is belonging to which client request. If the “ welcome” endpoint is accessed by multiple clients, you will see a set of similar log entries (as above log entry) in the log file. 22:24:34.171 INFO 42251 - c.s.e.s.m.s.c.WelcomeController : inside the welcomeMessage If you look at the application log, you will notice the below log entry. Then access the /welcome endpoint as follows. You can use following command to run the application. Now run the spring boot application and access the /welcome endpoint. Then create a simple controller as follows. Please follow the instructions given below. Lets look at some code examples with Spring Boot. If the underlying logging framework offers MDC functionality, then SLF4J will delegate to the underlying framework’s MDC. SLF4J supports MDC, or mapped diagnostic context. MDC data can also be highly helpful in filtering messages or triggering certain actions. Mapped Diagnostic Context” is essentially a map maintained by the logging framework where the application code provides key-value pairs which can then be inserted by the logging framework in log messages. Mapped Diagnostic Context (MDC) is used to enhance the application logging by adding some meaningful information to log entries. If we are going add this manually, this will be a tedious and repetitive work that consumes more time and resources.ĭont worry! This can be done within few seconds with MDC (Mapped Diagnostic Context) support of the logging framework that you are using. Therefore we need to make sure that client identifier is added to the each and every log statements of the application.Īssume that the application contains thousands of log entries (even more) in hundred of source files. To avoid the mix up of the log statements, we can add a client identifier (anything that can be uniquely identify the client) to the log statements. How to differentiate log statements with respective to each clients? This’ll make it difficult to trace and debug if any processing error occurred in MyServlet life cycle. And when this servlet is serving more than one clients at the same time, the log statements will be mixed and there’s no way to differentiate which log statement is belongs to which client’s processing. With the above said configuration, all the log messages from MyServlet will go into a single log file. A file appender has been defined for this servlet, so all the log messages will be logged into a text file. And, this servlet uses log4j framework for logging. Before I explain what is MDC, lets assume that we are going to develop a simple web application with one servlet MyServlet that serves requests from multiple clients. SLF4J allows the end-user to plug in the desired logging framework at deployment time. The Simple Logging Facade for Java ( SLF4J) serves as a simple facade or abstraction for various logging frameworks, such as, logback and log4j. If you need to brush up your knowledge on SLF4J, here it is the time. Here we are going to look at the MDC feature of the logging framework. I believe that SLF4J is not a new concept for most of the java developers. ![]()
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