Log4j How to configure simplest possible file logging

Question

My story   I want to make a thing which is as simple as a  simplest possible log4j logger that logs rows to a file  I have found several examples with some functionality  but not a basic  general one that really works  and not one with an explanation how the each row work   Question   Could anybody provide one   Prerequisites         I already know where to put the file and I have the log4j configured and working for console logging    Now I want to log to a file and also find the file from file system once the program has run    Rows needed to be added to the existing log4j properties file are the desired output

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lt  xml version  1 0  encoding  UTF-8   gt   lt  DOCTYPE log4j configuration SYSTEM  log4j dtd  gt    lt log4j configuration xmlns log4j  http   jakarta apache org log4j   debug  false  gt       lt appender name  fileAppender  class  org apache log4j RollingFileAppender  gt         lt param name  Threshold  value  INFO    gt         lt param name  File  value  sample log   gt         lt layout class  org apache log4j PatternLayout  gt            lt param name  ConversionPattern  value   d  -5p    c 1    m  n    gt         lt  layout gt      lt  appender gt      lt root gt        lt priority value   debug    gt        lt appender-ref ref  fileAppender    gt      lt  root gt     lt  log4j configuration gt    Log4j can be a bit confusing  So lets try to understand what is going on in this file  In log4j you have two basic constructs appenders and loggers    Appenders define how and where things are appended  Will it be logged to a file  to the console  to a database  etc    In this case you are specifying that log statements directed to fileAppender will be put in the file sample log using the pattern specified in the layout tags  You could just as easily create a appender for the console or the database  Where the console appender would specify things like the layout on the screen and the database appender would have connection details and table names    Loggers respond to logging events as they bubble up  If an event catches the interest of a specific logger it will invoke its attached appenders  In the example below you have only one logger the root logger - which responds to all logging events by default  In addition to the root logger you can specify more specific loggers that respond to events from specific packages  These loggers can have their own appenders specified using the appender-ref tags or will otherwise inherit the appenders from the root logger  Using more specific loggers allows you to fine tune the logging level on specific packages or to direct certain packages to other appenders   So what this file is saying is    Create a fileAppender that logs to file sample log Attach that appender to the root logger  The root logger will respond to any events at least as detailed as  debug  level The appender is configured to only log events that are at least as detailed as  info    The net out is that if you have a logger debug  blah blah   in your code it will get ignored  A logger info  Blah blah    will output to sample log   The snippet below could be added to the file above with the log4j tags  This logger would inherit the appenders from  lt root gt  but would limit the all logging events from the package org springframework to those logged at level info or above      lt  -- Example Package level Logger -- gt       lt logger name  org springframework  gt           lt level value  info   gt       lt  logger gt

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Here s a simple one that I often use     Set up logging to include a file record of the output   Note  the file is always created  even if there is    no actual output  log4j rootLogger error  stdout  R    Log format to standard out log4j appender stdout org apache log4j ConsoleAppender log4j appender stdout layout org apache log4j PatternLayout log4j appender stdout layout ConversionPattern     5p t  d    t    F  L  n      t m n n    File based log output log4j appender R org apache log4j RollingFileAppender log4j appender R File owls conditions log log4j appender R MaxFileSize 10000KB   Keep one backup file log4j appender R MaxBackupIndex 1 log4j appender R layout org apache log4j PatternLayout log4j appender R layout ConversionPattern     5p t  d    t    F  L  n      t m n n   The format of the log is as follows   ERROR    2009-09-13 09 56 01 760   main   RDFDefaultErrorHandler java 44          http   www xfront com owl ontologies camera   line 1 column 1   Content is not allowed in prolog    Such a format is defined by the string  5p t  d    t    F  L  n      t m n n  You can read the meaning of conversion characters in log4j javadoc for PatternLayout   Included comments should help in understanding what it does  Further notes    it logs both to console and to file  in this case the file is named owls conditions log  change it according to your needs  files are rotated when they reach 10000KB  and one back-up file is kept

User · Answer

I have one generic log4j xml file for you    lt  xml version  1 0  encoding  iso-8859-1   gt   lt  DOCTYPE log4j configuration SYSTEM  log4j dtd   gt   lt log4j configuration debug  false  gt        lt appender name  default console  class  org apache log4j ConsoleAppender  gt           lt param name  target  value  System out    gt           lt param name  threshold  value  debug    gt           lt layout class  org apache log4j PatternLayout  gt               lt param name  ConversionPattern  value   d ISO8601   -5p   c 1   -  m n    gt           lt  layout gt       lt  appender gt        lt appender name  default file  class  org apache log4j FileAppender  gt           lt param name  file  value   log mylogfile log    gt           lt param name  append  value  false    gt           lt param name  threshold  value  debug    gt           lt layout class  org apache log4j PatternLayout  gt               lt param name  ConversionPattern  value   d ISO8601   -5p   c 1   -  m n    gt           lt  layout gt       lt  appender gt        lt appender name  another file  class  org apache log4j FileAppender  gt           lt param name  file  value   log anotherlogfile log    gt           lt param name  append  value  false    gt           lt param name  threshold  value  debug    gt           lt layout class  org apache log4j PatternLayout  gt               lt param name  ConversionPattern  value   d ISO8601   -5p   c 1   -  m n    gt           lt  layout gt       lt  appender gt        lt logger name  com yourcompany SomeClass  additivity  false  gt           lt level value  debug    gt           lt appender-ref ref  another file    gt       lt  logger gt        lt root gt           lt priority value  info    gt           lt appender-ref ref  default console    gt           lt appender-ref ref  default file    gt       lt  root gt   lt  log4j configuration gt    with one console  two file appender and one logger poiting to the second file appender instead of the first   EDIT  In one of the older projects I have found a simple log4j properties file     For the general syntax of property based configuration files see   the documentation of org apache log4j PropertyConfigurator     The root category uses two appenders  default out and default file    The first one gathers all log output  the latter only starting with    the priority INFO    The root priority is DEBUG  so that all classes can be logged unless    defined otherwise in more specific properties  log4j rootLogger DEBUG  default out  default file    System out println appender for all classes log4j appender default out org apache log4j ConsoleAppender log4j appender default out threshold DEBUG log4j appender default out layout org apache log4j PatternLayout log4j appender default out layout ConversionPattern  -5p  c   m n  log4j appender default file org apache log4j FileAppender log4j appender default file append true log4j appender default file file  log mylogfile log log4j appender default file threshold INFO log4j appender default file layout org apache log4j PatternLayout log4j appender default file layout ConversionPattern  -5p  c   m n   For the description of all the layout arguments look here  log4j PatternLayout arguments

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Here is a log4j properties file that I ve used with great success   logDir  var log myapp  log4j rootLogger INFO  stdout  log4j rootLogger DEBUG  stdout  log4j appender stdout org apache log4j DailyRollingFileAppender log4j appender stdout layout org apache log4j PatternLayout log4j appender stdout layout ConversionPattern  d MM dd yyyy hh mm ss a   -5p  -30c 1    m n log4j appender stdout DatePattern    yyyy-MM-dd log4j appender stdout File   logDir  myapp log log4j appender stdout append true   The DailyRollingFileAppender will create new files each day with file names that look like this   myapp log 2017-01-27 myapp log 2017-01-28 myapp log 2017-01-29 myapp log   lt -- today s log   Each entry in the log file will will have this format   01 30 2017 12 59 47 AM INFO  Component1     calling foobar    userId 123  returning totalSent 1 01 30 2017 12 59 47 AM INFO  Component2     count 1  gt  0  calling fooBar     Set the location of the above file by using -Dlog4j configuration  as mentioned in this posting   java -Dlog4j configuration file  home myapp config log4j properties com foobar myapp   In your Java code  be sure to set the name of each software component when you instantiate your logger object  I also like to log to both the log file and standard output  so I wrote this small function   private static final Logger LOGGER   Logger getLogger  Component1     public static void log org apache log4j Logger logger  String message         logger info message       System out printf   s n   message      public static String stackTraceToString Exception ex        StringWriter sw   new StringWriter        PrintWriter pw   new PrintWriter sw       ex printStackTrace pw       return sw toString        And then call it like so   LOGGER info String format  Exception occurred   s   stackTraceToString ex

[java] Log4j: How to configure simplest possible file logging?

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