Log4j ConsoleAppender Configuration Example

Any logging application intended to print the logging information to a console should use the org.apache.log4j.ConsoleAppender. Console Appender is a simple class designed to write the logging information to either System.out or System.err.

In this example, we will try to show how to use the org.apache.log4j.ConsoleAppender to print the logs in the application console using the Log4j logging services.

1. Introduction

Printing messages to the console is an integral part of the development testing and the debugging of a Java program. If developers are working on a Server side application, where they cannot see what’s going on inside the server, then their only visibility tool is a log file.

Without logs, developers cannot do any debugging or see what’s going on inside the application. Though, Java has pretty handy System.out.println() methods to print something on console, which can also be routed to log file but not sufficient for a real-world Java application.

If developers are running a Java program in Linux or Unix based systems, Log4j or SLF4j or any other logging framework offer a lot features, flexibility, and improvement on message quality, which is not possible using the System.out.println() statements.

1.1 What is Log4j?

Log4j is a simple, flexible, and fast Java-based logging framework. It is thread-safe and supports internationalization. We mainly have 3 components to work with Log4j:

  • Logger: It is used to log the messages.
  • Appender: It is used to publish the logging information to the destination like a file, database, console etc.
  • Layout: It is used to format logging information in different styles.

1.1.1 Log4j Logger Class

Logger class provides the methods for the logging process. We can use the getLogger() method to get the Logger object. The syntax is given below:

static Logger log = Logger.getLogger(YourClassName.class);

Logger class has 5 logging methods which are used to print the status of an application:

DescriptionMethod Syntax
debug(Object message)It is used to print the message with the level org.apache.log4j.Level.DEBUG.public void debug(Object message)
error(Object message)It is used to print the message with the level org.apache.log4j.Level.ERROR.public void error(Object message)
info(Object message)It is used to print the message with the level org.apache.log4j.Level.INFO.public void info(Object message)
fatal(Object message)It is used to print the message with the level org.apache.log4j.Level.FATAL.public void fatal(Object message)
warn(Object message)It is used to print the message with the level org.apache.log4j.Level.WARN.public void warn(Object message)
trace(Object message)It is used to print the message with the level org.apache.log4j.Level.TRACE.public void trace(Object message)

To summarize, the priority level is given below.

Trace < Debug < Info < Warn < Error < Fatal

Where org.apache.log4j.Level.FATAL has the highest priority and org.apache.log4j.Level.Trace has the lowest.

1.1.2 Log4j Appender Interface

Appender is an interface which is primarily responsible for printing the logging messages to the different destinations such as console, files, sockets, database etc. In Log4j we have different types of Appender implementation classes.

Fig. 1: Log4j Appender
Fig. 1: Log4j Appender

1.1.3 Log4j Layout Class

Layout component specifies the format in which the log statements are written into the destination repository by the Appender. In Log4j we have different types of Layout implementation classes.

Fig. 2: Log4j Layout
Fig. 2: Log4j Layout

1.2 Why prefer Log4j over System.out.println?

Below are some of the reasons, which are enough to understand the limitation of using System.out.println():

  • Any logging framework allows developers to log debugging information with a log level which can be used as filtering criteria, i.e. one can disable the message belongs to a particular log level. For e.g., Developers would be more concerned to see the WARN messages than DEBUG messages in the production environment
  • Logging framework can produce better outputs and metadata which helps to troubleshoot and debug. For e.g., Log4j allows to print formatted output by specifying a formatting pattern i.e. by using PatternLayout one can include a timestamp, class name etc

Now, open up the Eclipse IDE and let’s start building the application!

2. Log4j ConsoleAppender Configuration Example

Below are the steps involved in developing this application.

2.1 Tools Used

We are using Eclipse Kepler SR2, JDK 8, and Log4j Jar. Having said that, we have tested the code against JDK 1.7 and it works well.

2.2 Project Structure

Firstly, let’s review the final project structure, in case you are confused about where you should create the corresponding files or folder later!

Fig. 3: ConsoleAppender Application Project Structure
Fig. 3: Application Project Structure

2.3 Project Creation

This section will demonstrate on how to create a Java-based Maven project with Eclipse

Fig. 4: Create Maven Project
Fig. 4: Create Maven Project

In the New Maven Project window, it will ask you to select a project location. By default, ‘Use default workspace location‘ will be selected. Select the ‘Create a simple project (skip archetype selection)‘ checkbox and just click on next button to proceed.

Fig. 5: Project Details
Fig. 5: Project Details

It will ask you to ‘Enter the group and the artifact id for the project’. We will input the details as shown in the below image. The version number will be by default: 0.0.1-SNAPSHOT.

Fig. 6: Archetype Parameters
Fig. 6: Archetype Parameters

Click on finish and the creation of a maven project will be completed. If you observe, it has downloaded the maven dependencies and a pom.xml file will be created. It will have the following code:


<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

We can start adding the dependencies that developers want like Log4j, JUnit etc. Let’s start building the application!

3. Application Building

Below are the steps involved in developing this application.

3.1 Maven Dependencies

In this example, we are using the most stable Log4j version (i.e. log4j-1.2.17) in order to set-up the logging framework. The updated file will have the following code:


<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
		<!-- https://mvnrepository.com/artifact/log4j/log4j -->

3.2 Java Class Creation

Let’s create the required Java files. Right click on src/main/java folder, New -> Package.

Fig. 7: Java Package Creation
Fig. 7: Java Package Creation

A new pop window will open where we will enter the package name as: com.jcg.log4j.console.appender.

Fig. 8: Java Package Name (com.jcg.log4j.console.appender)
Fig. 8: Java Package Name (com.jcg.log4j.console.appender)

Once the package is created, we will need to create the implementation class. Right-click on the newly created package, New -> Class.

Fig. 9: Java Class Creation
Fig. 9: Java Class Creation

A new pop window will open and enter the file name as: Log4jDemo. The implementation class will be created inside the package: com.jcg.log4j.console.appender.

Fig. 10: Java Class (Log4jDemo.java)
Fig. 10: Java Class (Log4jDemo.java)

3.2.1 Implementation of Utility Class

Let’s write a quick Java program and write the logs in the console using Log4j configuration. Add the following code to it:


package com.jcg.log4j.console.appender;

import org.apache.log4j.Logger;

public class Log4jDemo {

	static Logger logger = Logger.getLogger(Log4jDemo.class);

	public static void main(String[] args) {

		// Logging The Output In The Console
		logger.debug("Hello! Log4j Console Appender Configuration Is Successfully Completed...!");

3.3 Log4j Configuration File

Log4j will be usually configured using a properties file or XML file. So once the log statements are in place, developers can easily control them using the external configuration file without modifying the source code.

The log4j.properties file is a Log4j configuration file which keeps properties in key-value pairs. By default, the LogManager looks for a file named log4j.properties in the CLASSPATH. To configure the logging framework, we need to implement a configuration file i.e. log4j.properties. Add the following code to it:


# Root Location Option !!

# Package Based Logging
# Redirect Log Messages To Console !!
log4j.appender.console.layout.conversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

Note: The configurable properties of ConsoleAppender are described below:

immediateFlushUsed to set if the console stream being flushed with each logging output request.
encodingUsed to override the default character-encoding scheme.
targetUsed to print either System.out or System.err. The default is System.out.

4. Run the Application

To run the application, Right click on the Log4jDemo class, Run As -> Java Application. Developers can debug the example and see what happens after every step. Enjoy!

Fig. 11: Run Application
Fig. 11: Run Application

5. Project Demo

When we will execute the example the output will be displayed on the console.

Fig. 12: Logging Output
Fig. 12: Logging Output

That’s all for this post. Happy Learning!!

6. Conclusion

That’s all for getting the developers started with the Log4j example. We will look into more features in the next posts. I hope this article served you whatever you were looking for. Developers can download the sample application as an Eclipse project in the Downloads section.

7. Download the Eclipse Project

This was an example of Log4j Console Appender.

You can download the full source code of this example here: Log4jConsoleAppender


An experience full-stack engineer well versed with Core Java, Spring/Springboot, MVC, Security, AOP, Frontend (Angular & React), and cloud technologies (such as AWS, GCP, Jenkins, Docker, K8).
Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Inline Feedbacks
View all comments
Back to top button