# LOG4J : Configuration for Java

By

Paul Tomoiu

●

In 

Logging, 

log4j, 

Examples

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Published 2022-12-03

This tutorial explains to you how to configure the LOG4J for Java. This tutorial is using Eclipse and Maven. This is for a simple Java application.

Log4j is a Java library that is used for logging. Here is the architecture overview of log4j framework:

Here are some good things to know regarding the log4j architecture:

• The log4j Logger object is responsible for capturing logging information
• Each Logger is independently configurable
• A Logger can send log messages to multiple Appenders
• The log4j Layout object is used to format logging information (we can get "one-line-at-a-time", XML, HTML, JSON and other formats)
• The log4j Appender object is responsible for writing (publishing) logging information to various destinations such as a files, databases, JMS, console, UNIX Syslog, etc.
• The log4j Filters can be defined on configuration files to give more fine-grained control over the logging information (burst filters, time filters for instance). The BurstFilter is a logging filter that regulates logging traffic.
• The log4j ObjectRenderer is provides a String representation of different objects passed to the logging framework. This object is used by log4j Layout objects.
• The log4j LogManager read the initialization parameters and manage the log4j framework

Here are the steps for configuring an existing Maven Java application for using log4j:

• Add the following in pom.xml :

 <dependencies>
      <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
      </dependency>
</dependencies>

• Build the project using Maven in order to obtain the oc4j libraries.

• Create a directory "resource" (for instance) under src folder

• Create the log4j.properties file in it.

Here is the log4j.properties content:

# Root logger option
log4j.rootLogger=INFO, stdout, file

# Log the messages to the console
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

# Log the messages to a log file with file rolling
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=C:\\JAVA\\log4j-application.log
log4j.appender.file.MaxFileSize=4MB
log4j.appender.file.MaxBackupIndex=10
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

When you run your project, configure the CLASSPATH and add the location of the log4j.properties files by clicking on:

Run As -> Run Configuration -> Classpath tab -> click on User Entries -> Advanced -> select Add Folder -> select the location of your log4j.properties file and then -> OK -> Run.

Now you can use log4j using a basic configuration. If you want you can extend the functionalities of log4j.