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logging: Example That Sets Up Different Logging Levels

The logging quickstart demonstrates how to configure different logging levels in WildFly. It also includes an asynchronous logging example.

What is it?

The logging quickstart demonstrates how to set up and log different levels of information in WildFly Application Server. An example of asynchronous logging is also included in the configuration examples.

This quickstart contains just one class file and one JSP file. When you access the application, it fires off the logging information.

To better visualize how the logging configuration works, you first deploy and access the application before configuring the logs and view the resulting log files. Then you configure the logs, redeploy and access the application, and look at the log files again to see the differences.

Access the Application

The application is running at the following URL: http://localhost:8080/{artifactId}/.

You will see the following message in the server console:

FATAL [org.jboss.as.quickstarts.logging.LoggingExample] (default task-1) THIS IS A FATAL MESSAGE
ERROR [org.jboss.as.quickstarts.logging.LoggingExample] (default task-1) THIS IS AN ERROR MESSAGE
WARN  [org.jboss.as.quickstarts.logging.LoggingExample] (default task-1) THIS IS A WARNING MESSAGE
INFO  [org.jboss.as.quickstarts.logging.LoggingExample] (default task-1) THIS IS AN INFO MESSAGE
ERROR [org.jboss.as.quickstarts.logging.LoggingExample] (default task-1) THIS IS AN ERROR MESSAGE
FATAL [org.jboss.as.quickstarts.logging.LoggingExample] (default task-1) THIS IS A FATAL MESSAGE
INFO  [org.jboss.as.quickstarts.logging.LoggingExample] (default task-1) THIS IS AN INFO MESSAGE
WARN  [org.jboss.as.quickstarts.logging.LoggingExample] (default task-1) THIS IS A WARNING MESSAGE

Check the Server Logs

The log files are located in the WILDFLY_HOME/standalone/log log directory. At this point you should see the following log files.

  • server.log - This is the standard log produced by the application server. By default, it contains all the server log messages, including the server startup messages.

  • gc.log.0.current - This is a garbage collection log. It contains garbage collection activity and can be used for diagnostic purposes. This log can be ignored as it is not used in this quickstart.

Configure the Server

Now you have deployed the quickstart with the default configuration, you run a management CLI script to configure the logging subsystem and review the differences in the resulting log files.

  1. Before you begin, make sure you do the following:

  2. Review the configure-logging.cli file in the root of this quickstart directory. This script configures the logging subsytem in the server configuration file. It configures the periodic rotating file handlers and the async handlers, creates the logger for our quickstart class and sets the level to TRACE, and assigns the async handlers for our quickstart class.

  3. Open a new terminal, navigate to the root directory of this quickstart, and run the following command, replacing WILDFLY_HOME with the path to your server:

    $ WILDFLY_HOME/bin/jboss-cli.sh --connect --file=configure-logging.cli
    Note
    		 For Windows, use the WILDFLY_HOME\bin\jboss-cli.bat script.

    You should see the following result when you run the script:

    The batch executed successfully

Review the Modified Server Configuration

After stopping the server, open the WILDFLY_HOME/standalone/configuration/standalone.xml file and review the changes.

The following XML was added to the logging subsystem.

<async-handler name="TRACE_QS_ASYNC">
    <level name="TRACE"/>
    <queue-length value="1024"/>
    <overflow-action value="block"/>
    <subhandlers>
        <handler name="FILE_QS_TRACE"/>
    </subhandlers>
</async-handler>
<async-handler name="DEBUG_QS_ASYNC">
    <level name="DEBUG"/>
    <queue-length value="1024"/>
    <overflow-action value="block"/>
    <subhandlers>
        <handler name="FILE_QS_DEBUG"/>
    </subhandlers>
</async-handler>
<async-handler name="INFO_QS_ASYNC">
    <level name="INFO"/>
    <queue-length value="1024"/>
    <overflow-action value="block"/>
    <subhandlers>
        <handler name="FILE_QS_INFO"/>
    </subhandlers>
</async-handler>
<async-handler name="WARN_QS_ASYNC">
    <level name="WARN"/>
    <queue-length value="1024"/>
    <overflow-action value="block"/>
    <subhandlers>
        <handler name="FILE_QS_WARN"/>
    </subhandlers>
</async-handler>
<async-handler name="ERROR_QS_ASYNC">
    <level name="ERROR"/>
    <queue-length value="1024"/>
    <overflow-action value="block"/>
    <subhandlers>
        <handler name="FILE_QS_ERROR"/>
    </subhandlers>
</async-handler>
<async-handler name="FATAL_QS_ASYNC">
    <level name="FATAL"/>
    <queue-length value="1024"/>
    <overflow-action value="block"/>
    <subhandlers>
        <handler name="FILE_QS_FATAL"/>
    </subhandlers>
</async-handler>
...
<periodic-rotating-file-handler name="FILE_QS_TRACE">
    <file relative-to="jboss.server.log.dir" path="quickstart.trace.log"/>
    <suffix value=".yyyy.MM.dd"/>
</periodic-rotating-file-handler>
<periodic-rotating-file-handler name="FILE_QS_DEBUG">
    <file relative-to="jboss.server.log.dir" path="quickstart.debug.log"/>
    <suffix value=".yyyy.MM.dd"/>
</periodic-rotating-file-handler>
<periodic-rotating-file-handler name="FILE_QS_INFO">
    <file relative-to="jboss.server.log.dir" path="quickstart.info.log"/>
    <suffix value=".yyyy.MM.dd"/>
</periodic-rotating-file-handler>
<periodic-rotating-file-handler name="FILE_QS_WARN">
    <file relative-to="jboss.server.log.dir" path="quickstart.warn.log"/>
    <suffix value=".yyyy.MM.dd"/>
</periodic-rotating-file-handler>
<periodic-rotating-file-handler name="FILE_QS_ERROR">
    <file relative-to="jboss.server.log.dir" path="quickstart.error.log"/>
    <suffix value=".yyyy.MM.dd"/>
</periodic-rotating-file-handler>
<periodic-rotating-file-handler name="FILE_QS_FATAL">
    <file relative-to="jboss.server.log.dir" path="quickstart.fatal.log"/>
    <suffix value=".yyyy.MM.dd"/>
</periodic-rotating-file-handler>
...
<logger category="org.jboss.as.quickstarts.logging">
    <level name="TRACE"/>
    <handlers>
        <handler name="TRACE_QS_ASYNC"/>
        <handler name="DEBUG_QS_ASYNC"/>
        <handler name="INFO_QS_ASYNC"/>
        <handler name="WARN_QS_ASYNC"/>
        <handler name="ERROR_QS_ASYNC"/>
        <handler name="FATAL_QS_ASYNC"/>
    </handlers>
</logger>

Recheck the Server Logs

The log files are located in the WILDFLY_HOME/standalone/log log directory. You should now see 8 log files.

  • The following logs are the standard log files produced by the application server:

    • server.log - The standard log produced by the application server.

    • gc.log.0.current - The garbage collection log can be ignored as it is not used in this quickstart.

  • The following logs are produced by the quickstart. They are listed below in hierarchical order from the largest file containing the most messages to the smallest file containing the least messages.

    • quickstart.trace.log

    • quickstart.debug.log

    • quickstart.info.log

    • quickstart.warn.log

    • quickstart.error.log

    • quickstart.fatal.log

The following describes what happens when you access this quickstart:

  1. The application class file fires off logs of the various types (INFO, DEBUG, TRACE, WARN, ERROR, FATAL). Each log message goes to a different file, as defined in the standalone.xml file. Also notice in the standalone.xml that the application package defines its own log level.

  2. The class file demonstrates the usage of log guards. Log guards are a development best practice. Simply put, instead of just writing out logs, we wrap the log writes in a check for that log level being enabled. While this may seem like overhead, that boolean check is more efficient than relying on the underlying framework to do the check at write time.

  3. Finally, the class file logs various levels, each to its own file as configured in standalone.xml. Note that log levels are hierarchical. When set, all log levels above the specified level are logged as well.

  4. Common uses of the 6 log levels are outlined below. You should use the level that makes the most sense in your environment.

    FATAL - Used to track critical system failures.  When this log message is written, it is writing application error that has caused service to cease.  This is the most narrow logging.
ERROR - Used to track application errors that may cause one request to fail (not a service ceasement).
WARN - This is setting is used in most production environments.  At this level, all *WARN*, *ERROR*, and *FATAL* messages are written.  Use this level message  as a predictive measure for possible forthcoming issues.
INFO - Usually only used in a development environment.  This provides any information - state transition, object values, etc
DEBUG - Turned on in any environment when a problem is occuring.  The information captured may be throughput, communication, object values, etc.
TRACE - Turned on in any environment where you are trying to follow an execution path, for optimization or debugging.  This is the most broad logging level and all messages are written.

  5. To view log file differences for different logging levels, change the level for the "org.jboss.as.quickstarts.logging" logger from TRACE to DEBUG, INFO, WARN, ERROR, or FATAL, then access the application.

This script removes the log and file handlers from the logging subsystem in the server configuration. You should see the following result when you run the script:

The batch executed successfully