Dynamically Changing log4j log level

Question

What are the different approaches for changing the log4j log level dynamically  so that I will not have to redeploy the application  Will the changes be permanent in those cases

User · Answer

Log4j2 can be configured to refresh its configuration by scanning the log4j2.xml file (or equivalent) at given intervals. Just add the "monitorInterval" parameter to your configuration tag. See line 2 of the sample log4j2.xml file, which tells log4j to to re-scan its configuration if more than 5 seconds have passed since the last log event.

<?xml version="1.0" encoding="UTF-8" ?>
<Configuration status="warn" monitorInterval="5" name="tryItApp" packages="">

    <Appenders>
        <RollingFile name="MY_TRY_IT"
                     fileName="/var/log/tryIt.log"
                     filePattern="/var/log/tryIt-%i.log.gz">
            <Policies>
                <SizeBasedTriggeringPolicy size="25 MB"/>
            </Policies>
            ...
        </RollingFile>
    </Appenders>


    <Loggers>
        <Root level="error">
            <AppenderRef ref="MY_TRY_IT"/>
        </Root>
    </Loggers>

</Configuration>

There are extra steps to make this work if you are deploying to a tomcat instance, inside an IDE, or when using spring boot. That seems somewhat out of scope here and probably merits a separate question.

User · Answer

With log4j 1 x I find the best way is to use a DOMConfigurator to submit one of a predefined set of XML log configurations  say  one for normal use and one for debugging    Making use of these can be done with something like this     public static void reconfigurePredefined String newLoggerConfigName        String name   newLoggerConfigName toLowerCase        if   default  equals name           name    log4j xml         else         name    log4j-    name     xml              if  Log4jReconfigurator class getResource       name     null          String logConfigPath   Log4jReconfigurator class getResource       name  getPath          logger warn  Using log4j configuration      logConfigPath         try  InputStream defaultIs   Log4jReconfigurator class getResourceAsStream       name             new DOMConfigurator   doConfigure defaultIs  LogManager getLoggerRepository             catch  IOException e            logger error  Failed to reconfigure log4j configuration  could not find file     logConfigPath     on the classpath   e           catch  FactoryConfigurationError e            logger error  Failed to reconfigure log4j configuration  could not load file     logConfigPath  e                 else         logger error  Could not find log4j configuration file     name     xml on classpath                Just call this with the appropriate config name  and make sure that you put the templates on the classpath

User · Answer

If you would want to change the logging level of all the loggers use the below method  This will enumerate over all the loggers and change the logging level to given level  Please make sure that you DO NOT have log4j appender loggerName Threshold DEBUG property set in your log4j properties file   public static void changeLogLevel Level level        Enumeration lt   gt  loggers   LogManager getCurrentLoggers        while loggers hasMoreElements              Logger logger    Logger  loggers nextElement            logger setLevel level

User · Answer

Changing the log level is simple  modifying other portions of the configuration will pose a more in depth approach   LogManager getRootLogger   setLevel Level DEBUG     The changes are permanent through the life cyle of the Logger  On reinitialization the configuration will be read and used as setting the level at runtime does not persist the level change   UPDATE  If you are using Log4j 2 you should remove the calls to setLevel per the documentation as this can be achieved via implementation classes      Calls to logger setLevel   or similar methods are not supported in the   API  Applications should remove these  Equivalent functionality is   provided in the Log4j 2 implementation classes but may leave the   application susceptible to changes in Log4j 2 internals

User · Answer

You can use following code snippet    ch qos logback classic Logger LoggerFactory getLogger packageName   setLevel ch qos logback classic Level toLevel logLevel

User · Answer

This answer won t help you to change the logging level dynamically  you need to restart the service  if you are fine restarting the   service  please use the below solution   I did this to Change log4j log level and it worked for me  I have n t referred any document  I used this system property value to set my logfile name  I used the same technique to set logging level as well  and it worked   passed this as JVM parameter  I use Java 1 7   Sorry this won t dynamically change the logging level  it requires a restart of the service  java -Dlogging level DEBUG -cp xxxxxx jar  xxxxx java   in the log4j properties file  I added this entry   log4j rootLogger   logging level  file stdout   I tried    java -Dlogging level DEBUG -cp xxxxxx jar  xxxxx java  java -Dlogging level INFO-cp xxxxxx jar  xxxxx java  java -Dlogging level OFF -cp xxxxxx jar  xxxxx java   It all worked  hope this helps   I have these following dependencies in my pom xml   lt dependency gt               lt groupId gt log4j lt  groupId gt               lt artifactId gt log4j lt  artifactId gt               lt version gt 1 2 17 lt  version gt   lt  dependency gt    lt dependency gt       lt groupId gt log4j lt  groupId gt       lt artifactId gt apache-log4j-extras lt  artifactId gt       lt version gt 1 2 17 lt  version gt   lt  dependency gt

User · Answer

For log4j 2 API   you can use   Logger logger   LogManager getRootLogger    Configurator setAllLevels logger getName    Level getLevel level

User · Answer

File Watchdog  Log4j is able to watch the log4j xml file for configuration changes  If you change the log4j file  log4j will automatically refresh the log levels according to your changes  See the documentation of org apache log4j xml DOMConfigurator configureAndWatch String long  for details  The default wait time between checks is 60 seconds  These changes would be persistent  since you directly change the configuration file on the filesystem  All you need to do is to invoke DOMConfigurator configureAndWatch   once   Caution  configureAndWatch method is unsafe for use in J2EE environments due to a Thread leak  JMX  Another way to set the log level  or reconfiguring in general  log4j is by using JMX  Log4j registers its loggers as JMX MBeans  Using the application servers MBeanServer consoles  or JDK s jconsole exe  you can reconfigure each individual loggers  These changes are not persistent and would be reset to the config as set in the configuration file after you restart your application  server    Self-Made  As described by Aaron  you can set the log level programmatically  You can implement it in your application in the way you would like it to happen  For example  you could have a GUI where the user or admin changes the log level and then call the setLevel   methods on the logger  Whether you persist the settings somewhere or not is up to you

User · Answer

I have used this method with success to reduce the verbosity of the  org apache http  logs   ch qos logback classic Logger logger    ch qos logback classic Logger  LoggerFactory getLogger  org apache http    logger setLevel Level TRACE   logger setAdditive false

[java] Dynamically Changing log4j log level

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