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Posts Tagged ‘log4j’

Aggregating Error Logs to Send a Warning Email When Too Many of Them – Log4j, Stat4j, SMTPAppender

Posted by Jakub Holý on October 15, 2011

Our development team wanted to get notified as soon as something goes wrong in our production system, a critical Java web application serving thousands of customers daily. The idea was to let it send us an email when there are too many errors, indicating usually a problem with a database, an external web service, or something really bad with the application itself. In this post I want to present a simple solution we have implemented using a custom Log4J Appender based on Stats4j and an SMTPAppender (which is more difficult to configure and troubleshoot than you might expect) and in the following post I explore how to achieve the same effect with the open-source Hyperic HQ monitoring SW.

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Troubleshooting logging configuration (Log4j, commons-logging)

Posted by Jakub Holý on December 7, 2009

Did it ever happen to you that your logging didn’t behave as expected? Here are some tips how to find out what’s going on.

Commons-logging (since 1.1)

Set the system property org.apache.commons.logging.diagnostics.dest to STDOUT (or STDERR or a file name); docs: -Dorg.apache.commons.logging.diagnostics.dest=STDOUT

Extract of a sample output (no commons-logging.properties):

...
[LogFactory from sun.misc.Launcher$AppClassLoader@934873913] [ENV] Application classpath (java.class.path): ..
...
[LOOKUP] No properties file of name 'commons-logging.properties' found
....
Discovering a Log implementation...
...
Log adapter 'org.apache.commons.logging.impl.Log4JLogger' from classloader java.net.URLClassLoader@32689826 has been selected for use.

Extract of a sample output (incorrect commons-logging.properties found):

...
[LogFactory from sun.misc.Launcher$AppClassLoader@934873913] [LOOKUP] Properties file found at 'jar:file:/myproject/lib/test/dbunit-embeddedderby-parenttest-sources.jar!/commons-logging.properties' with priority 0.0
.. [LOOKUP] Properties file at 'file:/myproject/web/WEB-INF/classes/commons-logging.properties' with priority 0.0 does not override file at 'jar:file:/myproject/lib/test/dbunit-embeddedderby-parenttest-sources.jar!/commons-logging.properties' with priority 0.0
.. [LOOKUP] Properties file of name 'commons-logging.properties' found at 'jar:file:/myproject/lib/test/dbunit-embeddedderby-parenttest-sources.jar!/commons-logging.properties"
.. Attempting to load user-specified log class 'org.apache.commons.logging.impl.SimpleLog'...
.. Log adapter 'org.apache.commons.logging.impl.SimpleLog' from classloader sun.misc.Launcher$AppClassLoader@934873913 has been selected for use.
...

Notice that Commons Logging uses the context classloader and not e.g. Class.getClassloader() to locate the implementation to use, which may occassionally lead to some problems.

PS: You may be better of not using commons-logging because of its classloader issues. (SLF4J may be better?)

Log4j

Set the system property log4j.debug to true for Log4j to log the location of the configuration file it’s using and other useful information. You can also set it in in the log4j.properties file:

log4j.debug=true

Or, as mentioned above, pass it as a system property to Java, for example as in

java -Dlog4j.debug=true -jar YourApplication.jar

The debug information will be printed into the System.out, not in any log file you may have configured (Log4j can’t use itself for this logging).

Example output:

log4j: Parsing for [root] with value=[INFO, CONSOLE, filelog].
log4j: Level token is [INFO].
log4j: Category root set to INFO
log4j: Parsing appender named "CONSOLE".
log4j: Parsing layout options for "CONSOLE".
log4j: Setting property [conversionPattern] to [%6rms [%p] ..%0.46c %x- %m%n].
log4j: End of parsing for "CONSOLE".
log4j: Parsed "CONSOLE" options.
log4j: Parsing appender named "filelog".
log4j: Parsing layout options for "filelog".
log4j: Setting property [conversionPattern] to [%6rms [%p] ..%0.46c %x- %m%n].
log4j: End of parsing for "filelog".
log4j: Setting property [file] to [/home/me/mylog.log].
log4j: Setting property [maxBackupIndex] to [5].
log4j: Setting property [maxFileSize] to [50MB].
log4j: setFile called: /home/me/mylog.log, true
log4j: setFile ended
log4j: Parsed "filelog" options.
log4j: Parsing for [eu.ibacz.lqs.uiradrupdater] with value=[DEBUG].
log4j: Level token is [DEBUG].
log4j: Category eu.ibacz.lqs.uiradrupdater set to DEBUG
log4j: Handling log4j.additivity.eu.ibacz.lqs.uiradrupdater=[null]
log4j: Finished configuring.

For the log4j.properties:

log4j.rootCategory=INFO, CONSOLE, filelog

log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%6rms [%p] ..%0.46c %x- %m%n

log4j.appender.filelog=org.apache.log4j.RollingFileAppender
log4j.appender.filelog.File=${user.home}/mylog.log
log4j.appender.filelog.MaxFileSize=50MB
log4j.appender.filelog.MaxBackupIndex=5
log4j.appender.filelog.layout=org.apache.log4j.PatternLayout
log4j.appender.filelog.layout.ConversionPattern=%6rms [%p] ..%0.46c %x- %m%n

log4j.logger.eu.ibacz.lqs.uiradrupdater=DEBUG

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