How to initialize log4j properly?

Question

After adding log4j to my application I get the following output every time I execute my application:

log4j:WARN No appenders could be found for logger (slideselector.facedata.FaceDataParser).
log4j:WARN Please initialize the log4j system properly.

It seems this means a configuration file is missing. Where should this config file be located and what is a good start content?

I'm using plain java for developing a desktop application. So no webserver etc...

Answer 1

What are you developing in? Are you using Apache Tomcat?

log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.target=System.out
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{yyyyMMdd HH:mm:ss.SSS} [[%5p] %c{1} [%t]] %m%n

I have a properties like this in a Java app of mine.

Answer 2

Try to set debug attribut in log4j:configuration node to true.

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/" debug="true">

It prints out information as the configuration file is read and used to configure the log4j environment. You may be got more details to resolve your problem.

Answer 3

You can set up the log level by using setLevel().

The levels are useful to easily set the kind of informations you want the program to display.

For example:

Logger.getRootLogger().setLevel(Level.WARN); //will not show debug messages

The set of possible levels are:

TRACE,

DEBUG,

INFO,

WARN,

ERROR and

FATAL

According to Logging Services manual

Answer 4

If we are using apache commons logging wrapper on top of log4j, then we need to have both the jars available in classpath. Also, commons-logging.properties and log4j.properties/xml should be available in classpath.

We can also pass implementation class and log4j.properties name as JAVA_OPTS either using -Dorg.apache.commons.logging.Log=<logging implementation class name> -Dlog4j.configuration=<file:location of log4j.properties/xml file>. Same can be done via setting JAVA_OPTS in case of app/web server.

It will help to externalize properties which can be changed in deployment.

Answer 5

import org.apache.log4j.BasicConfigurator;

Call this method

BasicConfigurator.configure();

Answer 6

As per Apache Log4j FAQ page:

Why do I see a warning about "No appenders found for logger" and "Please configure log4j properly"?

This occurs when the default configuration files log4j.properties and log4j.xml can not be found and the application performs no explicit configuration. log4j uses Thread.getContextClassLoader().getResource() to locate the default configuration files and does not directly check the file system. Knowing the appropriate location to place log4j.properties or log4j.xml requires understanding the search strategy of the class loader in use. log4j does not provide a default configuration since output to the console or to the file system may be prohibited in some environments.

Basically the warning No appenders could be found for logger means that you're using log4j logging system, but you haven't added any Appenders (such as FileAppender, ConsoleAppender, SocketAppender, SyslogAppender, etc.) into your configuration file or the configuration file is missing.

There are three ways to configure log4j: with a properties file (log4j.properties), with an XML file and through Java code (rootLogger.addAppender(new NullAppender());).

log4j.properties

If you've property file present (e.g. when installing Solr), you need to place this file within your classpath directory.

classpath

Here are some command suggestions in Linux how to determine your classpath value:

$ echo $CLASSPATH
$ ps wuax | grep -i classpath
$ grep -Ri classpath /etc/tomcat? /var/lib/tomcat?/conf /usr/share/tomcat?

or from Java: System.getProperty("java.class.path").

Log4j XML

Below is a basic XML configuration file for log4j in XML format:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
  <appender name="console" class="org.apache.log4j.ConsoleAppender"> 
    <param name="Target" value="System.out"/> 
    <layout class="org.apache.log4j.PatternLayout"> 
      <param name="ConversionPattern" value="%-5p %c{1} - %m%n"/> 
    </layout> 
  </appender> 

  <root> 
    <priority value ="debug" /> 
    <appender-ref ref="console" /> 
  </root>

</log4j:configuration>

Tomcat

If you're using Tomcat, you may place your log4j.properties into: /usr/share/tomcat?/lib/ or /var/lib/tomcat?/webapps/*/WEB-INF/lib/ folder.

Solr

For the reference, Solr default log4j.properties file looks like:

#  Logging level
solr.log=logs/
log4j.rootLogger=INFO, file, CONSOLE

log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender

log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%-4r [%t] %-5p %c %x \u2013 %m%n

#- size rotation with log cleanup.
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.MaxFileSize=4MB
log4j.appender.file.MaxBackupIndex=9

#- File to log to and log format
log4j.appender.file.File=${solr.log}/solr.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%-5p - %d{yyyy-MM-dd HH:mm:ss.SSS}; %C; %m\n

log4j.logger.org.apache.zookeeper=WARN
log4j.logger.org.apache.hadoop=WARN

# set to INFO to enable infostream log messages
log4j.logger.org.apache.solr.update.LoggingInfoStream=OFF

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Why can't log4j find my properties file in a J2EE or WAR application?

The short answer: the log4j classes and the properties file are not within the scope of the same classloader.

Log4j only uses the default Class.forName() mechanism for loading classes. Resources are handled similarly. See the documentation for java.lang.ClassLoader for more details.

So, if you're having problems, try loading the class or resource yourself. If you can't find it, neither will log4j. ;)

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See also:

• Short introduction to log4j at Apache site
• Apache: Logging Services: FAQ at Apache site