Logging Activity – Log4j Sensitive Data Masking

Overview

Logging Activity is a Spring Boot application created to experiment with masking sensitive data in logs using Log4j

This project demonstrates how sensitive information can be masked at the logging framework level (not in business logic) using a reusable utility dependency.

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Application Details

• Application Name: logging-activity
• Application Framework: Spring Boot
• Base Package: in.org.nnm
• Logging Framework: Log4j
• Primary Goal: Mask sensitive data in application logs

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Project Structure

│in.org.nnm
├── src/main/java
│   ├── controller
│   │   └── LoggingController.java
│   │       └── Endpoint: GET /logging/display
│   │
│   └── utils
│       └── csvparser
│           └── display()
│               └── Reads logs from a TXT file
│
├── src/main/resources
│   ├── log4j2-configurations
│   │   ├── log4j2.xml
│   │   ├── log4j2.yml
│   │   ├── log4j2.properties
│   │   └── log4j2.json
│   │
│   ├── logs.csv
│   └── application.properties
│
└── pom.xml

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External Dependency Used

This project uses a custom utility for Log4j masking:

<dependency>
    <groupId>in.org.nnm</groupId>
    <artifactId>log4j-utils</artifactId>
    <version>1.0.0</version>
</dependency>

Purpose of log4j-utils

• Centralized masking logic for Log4j
• Prevents sensitive data leakage in logs
• Reusable across multiple Spring Boot applications
• Keeps business code clean and secure

Sensitive Data Masking – Concept

1. Application generates logs normally
2. Log messages pass through Log4j layouts / rewrite policies
3. Masking logic from log4j-utils is applied
4. Sensitive data is replaced with masked values (e.g. ****)
5. Only masked logs are printed or stored

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Log4j Configuration Formats

This project includes four different Log4j configuration formats to experiment with and compare behavior while masking sensitive data.

File Name	Format
log4j2.xml	XML
log4j2.yml	YAML
log4j2.json	JSON
log4j2.properties	Properties

Each configuration file demonstrates:

• Console and JSON appenders
• Layout configurations
• Sensitive data masking support
• Different ways of defining Log4j settings

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Switching Log4j Configuration

You can switch between configurations by updating the following property in application.properties:

logging.config=classpath:log4j2-configurations/log4j2.xml

(Change the file name to test other formats)

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How to Run the Application

Prerequisites

• Java 17 or higher
• Maven
• Spring Boot

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Steps

git clone https://github.com/Neel1210/logging-activity.git
cd logging-activity
mvn clean install
mvn spring-boot:run

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API Endpoint

Once the application starts, access the endpoint at:

http://localhost:8080/logging/display

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Author

• Neelesh Mehar
• Software Engineer
• Focus areas: Java, Spring Boot, Logging, Security, Clean Architecture

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