Configuring Log4j Loggers Programmatically

Question

I am trying to use SLF4J  with log4j binding  for the first time   I would like to configure 3 different named Loggers that can be returned by a LoggerFactory which will log different levels and push the messages to different appenders    Logger 1  FileLogger  logs DEBUG and appends to DailyRollingFileAppender Logger 2  TracingLogger  logs TRACE  and appends to a JmsAppender Logger 3  ErrorLogger  logs ERROR  and appends to a different JmsAppender   Furthermore I want them configured programmatically  in Java  as opposed to XML or a log4j properties file    I imagine that  normally  I would define these Loggers somewhere in some bootstrapping code  like an init   method  However  because I want to use slf4j-log4j  I m confused about where I could define loggers and make them available to the classpath   I don t believe this is a violation of SLF4J s underlying purpose  as a facade   because my code using the SLF4J API won t ever know that these loggers exist  My code just makes normal calls to the SLF4J API  which then forwards them on to the log4j Loggers it finds on the classpath   But how do I configure those log4j Loggers on the classpath   in Java

User · Answer

It sounds like you re trying to use log4j from  both ends   the consumer end and the configuration end    If you want to code against the slf4j api but determine ahead of time  and programmatically  the configuration of the log4j Loggers that the classpath will return  you absolutely have to have some sort of logging adaptation which makes use of lazy construction   public class YourLoggingWrapper       private static boolean loggingIsInitialized   false       public YourLoggingWrapper                   blah            public static void debug String debugMsg            log LogLevel Debug  debugMsg                 Same for all other log levels your want to handle         You mentioned TRACE and ERROR       private static void log LogLevel level  String logMsg            if  loggingIsInitialized              initLogging             org slf4j Logger slf4jLogger   org slf4j LoggerFactory getLogger  DebugLogger             switch level            case  Debug              logger debug logMsg               break          default                 whatever                         log4j logging is lazily constructed  it gets initialized        the first time the invoking app calls a log method     private static void initLogging             loggingIsInitialized   true           org apache log4j Logger debugLogger   org apache log4j LoggerFactory getLogger  DebugLogger                Now all the same configuration code that  oers suggested applies               configure the logger  configure and add its appenders  etc          debugLogger addAppender someConfiguredFileAppender           With this approach  you don t need to worry about where when your log4j loggers get configured  The first time the classpath asks for them  they get lazily constructed  passed back and made available via slf4j  Hope this helped

User · Answer

You can add remove Appender programmatically to Log4j     ConsoleAppender console   new ConsoleAppender      create appender     configure the appender   String PATTERN     d   p  c  C 1    m n     console setLayout new PatternLayout PATTERN       console setThreshold Level FATAL     console activateOptions        add appender to any Logger  here is root    Logger getRootLogger   addAppender console      FileAppender fa   new FileAppender      fa setName  FileLogger      fa setFile  mylog log      fa setLayout new PatternLayout   d  -5p   c 1    m n       fa setThreshold Level DEBUG     fa setAppend true     fa activateOptions         add appender to any Logger  here is root    Logger getRootLogger   addAppender fa       repeat with all other desired appenders   I d suggest you put it into an init   somewhere  where you are sure  that this will be executed before anything else  You can then remove all existing appenders on the root logger with   Logger getRootLogger   getLoggerRepository   resetConfiguration      and start with adding your own  You need log4j in the classpath of course for this to work   Remark  You can take any Logger getLogger      you like to add appenders  I just took the root logger because it is at the bottom of all things and will handle everything that is passed through other appenders in other categories  unless configured otherwise by setting the additivity flag      If you need to know how logging works and how is decided where logs are written read this manual for more infos about that  In Short     Logger fizz   LoggerFactory getLogger  com fizz     will give you a logger for the category  com fizz   For the above example this means that everything logged with it will be referred to the console and file appender on the root logger  If you add an appender to        Logger getLogger  com fizz   addAppender newAppender  then logging from fizz will be handled by alle the appenders from the root logger and the newAppender  You don t create Loggers with the configuration  you just provide handlers for all possible categories in your system

User · Answer

In the case that you have defined an appender in log4j properties and would like to update it programmatically  set the name in the log4j properties and get it by name   Here s an example log4j properties entry   log4j appender stdout Name console log4j appender stdout org apache log4j ConsoleAppender log4j appender stdout Target System out log4j appender stdout Threshold INFO   To update it  do the following     ConsoleAppender  Logger getRootLogger   getAppender  console    setThreshold Level DEBUG

User · Answer

If someone comes looking for configuring log4j2 programmatically in Java  then this link could help   https   www studytonight com post log4j2-programmatic-configuration-in-java-class   Here is the basic code for configuring a Console Appender   ConfigurationBuilder lt BuiltConfiguration gt  builder   ConfigurationBuilderFactory newConfigurationBuilder     builder setStatusLevel Level DEBUG      naming the logger configuration builder setConfigurationName  DefaultLogger        create a console appender AppenderComponentBuilder appenderBuilder   builder newAppender  Console    CONSOLE                    addAttribute  target   ConsoleAppender Target SYSTEM OUT      add a layout like pattern  json etc appenderBuilder add builder newLayout  PatternLayout                    addAttribute  pattern     d  p  c   t   m n     RootLoggerComponentBuilder rootLogger   builder newRootLogger Level DEBUG   rootLogger add builder newAppenderRef  Console      builder add appenderBuilder   builder add rootLogger   Configurator reconfigure builder build       This will reconfigure the default rootLogger and will also create a new appender

[java] Configuring Log4j Loggers Programmatically

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