Background

In our first Log4J sample, we relied on the default configuration.

Let us take another pebble step.

For this iteration, we will use a very small configuration file.

Lineage

1. Java:- JDK – Installing Java JDK on MS-Windows
   Link
2. HelloWorld In Java
   Link
3. Log4J – Preparation
   Link
4. HelloWorld In Log4J
   Link

Application

Class

helloLog4j.java

/*
    Import Apache log4j Packages
*/
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class helloLog4j
{

    /*
        Declare Variables
    */   
    static Logger log = null;
    
    public static void main(String[] args)
    {
       
        /*
            Declare Variables
        */
        Exception objExceptionNull = null;

        // configures the root logger
        log = LogManager.getRootLogger();  

        /*
            Get Logger passing on category
                category:- ClassName
        */    
        //log = LogManager.getLogger(helloLog4j.class);
    
        objExceptionNull = new NullPointerException("NullError");
        
        metadata();
        
        log.debug("Hello this is a debug message");

        log.info("Hello this is an info message");
        
        log.error
        (
              "Error Message Logged !!!"
            , objExceptionNull
        );
                
    } // function main
   
    
    static void metadata()
    {
       
        /*
            Declare Variables
        */
        String strLog4JVersion = null;
        String FORMAT_LOG4J_VERSION = "Log4j Version Number is %s %n";

        /*
            How can I check the version number of Log4j in a .jar file?
            Bhushan
            https://stackoverflow.com/questions/70333560/how-can-i-check-the-version-number-of-log4j-in-a-jar-file
        */
        
        /*
            Get log4J Version Number
        */
        strLog4JVersion
            = org.apache.log4j.Layout.class.getPackage().getImplementationVersion();
        
        /*
            If we have log4J Version Number, Log the retrieved version number
        */
        if (strLog4JVersion != null)
        {
                           
            System.out.printf
            (
                  FORMAT_LOG4J_VERSION
                , strLog4JVersion
            );
            
        }
       
   } //metadata
   
   
}

Configuration

log4j2.xml

Outline

1. Configuration
   • Attributes
     • status
       • Definition
         • This appender will not log any messages with priority lower than the one specified here even if the category’s priority is set lower.
         • This is useful to cut down the number of messages, for example, in a file log while displaying all messages on the console.
       • Sample
         • WARN
     • monitorInterval
       • The log file is checked every 30 seconds
       • If the file’s content has been changed, it is incorporated
2. Properties
   • Property
     • Attribute
       • name
         • LOG_PATTERN
     • Item
       • Pattern
         • Sample
           • %d{yyyy-MM-dd HH:mm:ss.SSS} %5p : %m%n%ex
         • Pattern Format
           • %d{yyyy-MM-dd HH:mm:ss.SSS}
           • %p
             • Message Priority ( FATAL, ERROR, WARN, INFO, DEBUG, or CUSTOM )
           • %m
             • Message
           • %n
             • New Line
           • %ex
             • Exception
3. Appenders
   • Console
     • Attribute
       • name
         • ConsoleAppender
       • target
         • SYSTEM_OUT
       • Follow
         • true
   • File
     • Attribute
       • fileName
         • Sample
           • logs\app.log
4. Loggers
   • Root
     • Attribute
       • level
         • info
     • AppenderRef
       • Attribute
         • ref
           • ConsoleAppender
           • FileAppender
   • Category
     • Attribute
       • level
         • info
     • AppenderRef
       • Attribute
         • ref
           • ConsoleAppender
           • FileAppender

File Content

<?xml version="1.0" encoding="UTF-8"?>

<Configuration 
    status="WARN" 
    monitorInterval="30"
    >
    
    <Properties>
        <Property name="LOG_PATTERN">
            %d{yyyy-MM-dd HH:mm:ss.SSS} %5p : %m%n%ex
        </Property>
    </Properties>
    
    <Appenders>
    
        <Console 
            name="ConsoleAppender" 
            target="SYSTEM_OUT" 
            follow="true"
        >
            <PatternLayout>
                <Pattern>${LOG_PATTERN}</Pattern>
            </PatternLayout>
        </Console>
        
        <File name="FileAppender" 
              fileName="logs\app.log"
        >
            <PatternLayout>
                <Pattern>${LOG_PATTERN}</Pattern>
            </PatternLayout>
        </File>
        
        
    </Appenders>
    
    <Loggers>

        <Root level="info">
        
            <AppenderRef 
                ref="ConsoleAppender" 
                />
            
            <AppenderRef 
                ref="FileAppender" 
                />
            
        </Root>
        
    </Loggers>
    
</Configuration>

 

Glossary

Pattern Format

 

Commended

Crediting Vipan Singla.

 

Referenced Materials

1. Vipan Singla
   • Don’t Use System.out.println!, Use Log4j
     Link