How do I set log4j level on the command line

Question

I want to add some log debug statements to a class I m working on  and I d like to see that in output when running the test  I d like to override the log4j properties on the command line  with something like this   -Dlog4j logger com mypackage Thingie DEBUG   I do this kind of thing frequently  I am specifically only interested in a way to pass this on the command line  I know how to do it with a config file  and that doesn t suit my workflow

User · Answer

As part of your jvm arguments you can set -Dlog4j.configuration=file:"<FILE_PATH>". Where FILE_PATH is the path of your log4j.properties file.

Please note that as of log4j2, the new system variable to use is log4j.configurationFile and you put in the actual path to the file (i.e. without the file: prefix) and it will automatically load the factory based on the extension of the configuration file:

-Dlog4j.configurationFile=/path/to/log4jconfig.{ext}

User · Answer

These answers actually dissuaded me from trying the simplest possible thing  Simply specify a threshold for an appender  say   console   in your log4j configuration like so   log4j appender console threshold   my logging threshold    Then  on the command line  include the system property -Dlog4j info -Dmy logging threshold INFO  I assume that any other property can be parameterized in this way  but this is the easiest way to raise or lower the logging level globally

User · Answer

Based on Thorbj  rn Ravn Andersens suggestion I wrote some code that makes this work  Add the following early in the main method and it is now possible to set the log level from the comand line  This have been tested in a project of mine but I m new to log4j and might have made some mistake  If so please correct me       Logger getRootLogger   setLevel Level WARN       HashMap lt String Level gt  logLevels new HashMap lt String Level gt         logLevels put  ALL  Level ALL       logLevels put  TRACE  Level TRACE       logLevels put  DEBUG  Level DEBUG       logLevels put  INFO  Level INFO       logLevels put  WARN  Level WARN       logLevels put  ERROR  Level ERROR       logLevels put  FATAL  Level FATAL       logLevels put  OFF  Level OFF       for String name System getProperties   stringPropertyNames             String logger  log4j logger            if name startsWith logger                String loggerName name substring logger length                 String loggerValue System getProperty name               if logLevels containsKey loggerValue                   Logger getLogger loggerName  setLevel logLevels get loggerValue                else                 Logger getRootLogger   warn  unknown log4j logg level on comand line    loggerValue

User · Answer

With Log4j2  this can be achieved using the following utility method added to your code   private static void setLogLevel       if  Boolean getBoolean  log4j debug          Configurator setLevel System getProperty  log4j logger    Level DEBUG           You need these imports  import org apache logging log4j Level  import org apache logging log4j core config Configurator    Now invoke the setLogLevel method in your main   or whereever appropriate and pass command line params -Dlog4j logger com mypackage Thingie and -Dlog4j debug true

User · Answer

In my pretty standard setup I ve been seeing the following work well when passed in as VM Option  commandline before class in Java  or VM Option in an IDE    -Droot log level TRACE

User · Answer

log4j does not support this directly   As you do not want a configuration file  you most likely use programmatic configuration   I would suggest that you look into scanning all the system properties  and explicitly program what you want based on this

User · Answer

Based on  lijat  here is a simplified implementation  In my spring-based application I simply load this as a bean   public static void configureLog4jFromSystemProperties       final String LOGGER PREFIX    log4j logger       for String propertyName   System getProperties   stringPropertyNames            if  propertyName startsWith LOGGER PREFIX           String loggerName   propertyName substring LOGGER PREFIX length           String levelName   System getProperty propertyName             Level level   Level toLevel levelName      defaults to DEBUG       if      equals levelName   amp  amp   levelName toUpperCase   equals level toString               logger error  Skipping unrecognized log4j log level     levelName      -D    propertyName         levelName           continue                logger info  Setting     loggerName       gt      level toString           Logger getLogger loggerName  setLevel level

[java] How do I set log4j level on the command line?

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