Using log4j in Tomcat and Solr and How to Make a Customized File Appender

This article shows how to use log4j for both tomcat and solr, besides that, I will also show you the steps to make your own customized log4j appender and use it in tomcat and solr. If you want more information than is found in this blogpost, feel free to visit our website or contact us.

Default Tomcat log mechanism

Tomcat by default uses a customized version of java logging api. The configuration is located at ${tomcat_home}/conf/logging.properties. It follows the standard java logging configuration syntax plus some special tweaks(prefix property with a number) for identifying logs of different web apps.

An example is below:

handlers = 1catalina.org.apache.juli.FileHandler, 2localhost.org.apache.juli.FileHandler, 3manager.org.apache.juli.FileHandler, 4host-manager.org.apache.juli.FileHandler, java.util.logging.ConsoleHandler

.handlers = 1catalina.org.apache.juli.FileHandler, java.util.logging.ConsoleHandler

1catalina.org.apache.juli.FileHandler.level = FINE

1catalina.org.apache.juli.FileHandler.directory = ${catalina.base}/logs

1catalina.org.apache.juli.FileHandler.prefix = catalina.

2localhost.org.apache.juli.FileHandler.level = FINE

2localhost.org.apache.juli.FileHandler.directory = ${catalina.base}/logs

2localhost.org.apache.juli.FileHandler.prefix = localhost.

Default Solr log mechanism

Solr uses slf4j logging, which is kind of wrapper for other logging mechanisms. By default, solr uses log4j syntax and wraps java logging api (which means that it looks like you are using log4j in the code, but it is actually using java logging underneath). It uses tomcat logging.properties as configuration file. If you want to define your own, it can be done by placing a logging.properties under ${tomcat_home}/webapps/solr/WEB-INF/classes/logging.properties

Switching to Log4j

Log4j is a very popular logging framework, which I believe is mostly due to its simplicity in both configuration and usage. It has richer logging features than java logging and it is not difficult to make an extension.

Log4j for tomcat

  1. Rename/remove ${tomcat_home}/conf/logging.properties
  2. Add log4j.properties in ${tomcat_home}/lib
  3. Add log4j-xxx.jar in ${tomcat_home}/lib
  4. Download tomcat-juli-adapters.jar from extras and put it into ${tomcat_home}/lib
  5. Download tomcat-juli.jar from extras and replace the original version in ${tomcat_home}/bin

(extras are the extra jar files for special tomcat installation, it can be found in the bin folder of a tomcat download location, fx. http://archive.apache.org/dist/tomcat/tomcat-6/v6.0.33/bin/extras/)

Log4j for solr

  1. Add log4j.properties in ${tomcat_home}/webapps/solr/WEB-INF/classes/ (create classes folder if not present)
  2. Replace slf4j-jdkxx-xxx.jar with slf4j-log4jxx-xxx.jar in ${tomcat_home}/webapps/solr/WEB-INF/lib (which means switching underneath implementation from java logging to log4j logging)
  3. Add log4jxxx.jar to ${tomcat_home}/webapps/solr/WEB-INF/lib

Make our own log4j file appender

Log4j has 2 types of common fileappender:

  • DailyRollingFileAppender – rollover at certain time interval
  • RollingFileAppender – rollover at certain size limit

And I found a nice customized file appender:

  •  CustodianDailyRollingFileAppender online.

I happen to need a file appender which should  rollover at certain time interverl(each day) and backup earlier logs in backup folder and get zipped. Plus removing logs older than certain days. CustodianDailyRollingFileAppender already has the rollover feature, so I decide to start with making a copy of this class,

Parameters

Besides the default parameters in DailyRollingFileAppender, I need 2 more parameters,

Outdir – backup directory

maxDaysToKeep – the number of days to keep the log file

You only need to define these 2 parameters in the new class, and add get/set methods for them (no constructor involved). The rest will be handled by log4j framework.

Logging entry point

When there comes a log event, the subAppend(…) function will be called, inside which a super.subAppend(event); will just do the log writing work. So before that function call, we can add the mechanism for back up and clean up.

Clean up old log

Use a file filter to find all log files start with the filename, delete those older than maxDaysToKeep.

Backup log

Make a separate Thread for zipping the log file and delete original log file afterwards(I found CyclicBarrier very easy to use for this type of wait thread to complete task, and a thread is preferable for avoiding file lock/access ect. problems). Call the thread at the point where current log file needs to be rolled over to backup.

Deploy the customized file appender

Let’s say we make a new jar called log4jxxappender.jar, we can deploy the appender by copying the jar file to ${tomcat_home}/lib and in ${tomcat_home}/webapps/solr/WEB-INF/lib

Example configuration for solr,

log4j.rootLogger=INFO, solrlog

log4j.appender.solrlog=com.findwise.xx.log4j.fileappender.YyRollingFileAppender

log4j.appender.solrlog.File=${catalina.home}/logs/solr.log

log4j.appender.solrlog.Append=true

log4j.appender.solrlog.Encoding=UTF-8

log4j.appender.solrlog.DatePattern='.'yyyy-MM-dd

log4j.appender.solrlog.MaxDaysToKeep=10

log4j.appender.solrlog.Outdir=${catalina.base}/logs/backup

log4j.appender.solrlog.layout=org.apache.log4j.PatternLayout

log4j.appender.solrlog.layout.ConversionPattern = %d [%t] %-5p %c - %m%n

Solr.war

Last thing to remember about solr is to zip the deployment folder ${tomcat_home}/webapps/solr and rename the zip file solr.zip to solr.war. Now you should have a log4j enabled solr.war file with your customized fileappender.

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