Through logging configuration in Mule, it is possible to configure what messages are logged, where they are logged, and how they are logged. By default, Mule uses asynchronous logging and only logs messages at the INFO level or higher using log4j2. The log4j2 configuration file can be customized to define the logging levels, categories, and synchronous or asynchronous logging.

1. Logging Configuration
In Mule

2.  There’s no need to state the importance of debuggers
for developers, and Mule developers are no exception.
The goal of this blog post is to provide you with a few
handy tips for debugging your custom Java code in Mule
Studio.

3.  Through the logging configuration it’s possible to configure what gets
logged, where it gets logged, and how it gets logged.
 Mule internally logs multiple messages along with some specific elements
in the application’s flows.
 The logger component can also be included to output any desired
messages.
 By creating a configuration file, it’s possible to define what kinds of
messages to log, in what way (asynchronously or synchronously), and
where they get logged (To console, To disk or to a database).
Logging Configuration In Mule

4.  For logging Mule uses slf4j.
 Slf4j is a logging facade, that discovers and uses a logging strategy from
the classpath, such as log4j2 or the JDK Logger.
 By Default Mule includes log4j2.
 The configuration used for it is log4j2.xml.
 The Mule server has a log4j2.xml file in the conf directory.
 This file can be customized when running the server in standalone mode.
Logging Configuration In Mule

5.  To view Anypoint Studio logs:
 Error Log :
 Logs can be viewed in Studio by clicking: Anypoint Studio > About Anypoint
Studio > Installation Details > Configuration tab > View Error Log
 Workspace Logs :
 The output from View Error Log is in the workspace’s ’.metadata/.log’ file
 Project Log:
 The logs for the mule application are present in the workspace’s
‘.mule/logs/<project>.log’ file.
Logging Configuration In Mule

6.  Types of logging :
 Synchronous :
 The execution of the thread that is processing the message is interrupted to wait for
the log message to be fully handled before it can continue.
 Asynchronous:
 The logging operation occurs in a separate thread, so the actual processing of your
message won’t be delayed to wait for the logging to complete.
 Note :
 By Default Mule uses the Asynchronous logging in the applications.
Logging Configuration In Mule

7. Synchronous Logging Asynchronous Logging
• Useful when Application logs are
required to be used as audit trails.
• The performance is low, as the
applications waits for the logger
component to complete the
logging.
• brings a substantial improvement
in throughput and latency of
message processing.
• after a system crash, a scenario is
possible where, some actions were
performed but not logged, since
log writing is performed on a
separate thread that runs
independently of other actions.
Logging Configuration In Mule

8.  By default, logging in Mule is done asynchronously and at a level greater
than or equal to INFO.
 Hence it ignores the messages at the DEBUG or TRACE level.
Logging Configuration In Mule

9.  Defining the Logging type, logging level or custom categories can be done
by modifying the log4j2.xml file.
 This file is located at different locations depending on the where the
application is running.
 In Standalone Mule Runtime :
 $MULE_HOME/conf/log4j2.xml
 In Anypoint Studio:
 src/main/resources
Logging Configuration In Mule

10.  If the file is not edited then the default
configuration is assumed for the application.
 The configuration can be overridden at the
domain or the application level.
 Create a custom file at a custom folder location
and point to it in the application’s deployment
properties.
 To point the application to use this file :
 open the application’s mule-deploy.properties file
in src/main/app and add a log.configFile property
with this location specified in it.
 Example :
log.configFile=myCustomFolder/myCustomlog4j2.xm
l
Logging Configuration In Mule

11.  If the deployment property is not set then mule searches for the config
file following child–first pattern as follows :
 Look for a file called log4j2-test.xml in the application
classpath
 Look for a file called log4j2.xml in the application
classpath
 Look for a file called log4j2-test.xml in the domain
classpath
 Look for a file called log4j2.xml in the domain classpath
 Look for a file called log4j2-test.xml in MULE_HOME/conf
 Look for a file called log4j2.xml in MULE_HOME/conf
 Apply default configuration.
Logging Configuration In Mule