File-based logging in Spring Boot - Mini Project: Build & Apply

File-based logging in Spring Boot

📖 Scenario: You are building a Spring Boot application that needs to keep track of important events and errors by writing logs to a file. This helps developers and system administrators understand what happened during the app's runtime.

🎯 Goal: Set up file-based logging in a Spring Boot application by creating a log file configuration, adding a log message in the code, and verifying the log output is written to the file.

📋 What You'll Learn

Create a Spring Boot application main class

Configure logging to write to a file named app.log

Add a log message using Spring Boot's logger

Run the application and verify the log message appears in app.log

💡 Why This Matters

🌍 Real World

File-based logging helps track application behavior and errors over time, which is essential for troubleshooting and monitoring in real-world software.

💼 Career

Understanding how to configure and use logging in Spring Boot is a key skill for backend developers and DevOps engineers to maintain reliable applications.

1

Create Spring Boot main application class

Create a Java class called LoggingApplication in package com.example.logging with a main method that starts the Spring Boot application using SpringApplication.run(LoggingApplication.class, args).

Spring Boot

package com.example.logging;

// Your code here

Need a hint?

This is the standard way to start a Spring Boot app. Use the @SpringBootApplication annotation and a main method.

2

Configure logging to write to a file

Create a file named src/main/resources/application.properties and add a property to set the logging file name to app.log using logging.file.name=app.log.

Spring Boot

package com.example.logging;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class LoggingApplication {
    public static void main(String[] args) {
        SpringApplication.run(LoggingApplication.class, args);
    }
}

# Your code here: Create application.properties with logging.file.name=app.log

Need a hint?

The application.properties file controls Spring Boot settings. Add logging.file.name=app.log to write logs to app.log.

3

Add a log message in the application

In the LoggingApplication class, add a private static final logger using LoggerFactory.getLogger(LoggingApplication.class). Then add a System.out.println line inside main to print "Application started" and a log info message with the same text using logger.info("Application started").

Spring Boot

package com.example.logging;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@SpringBootApplication
public class LoggingApplication {
    private static final Logger logger = LoggerFactory.getLogger(LoggingApplication.class);

    public static void main(String[] args) {
        SpringApplication.run(LoggingApplication.class, args);
        // Your code here: print and log "Application started"
    }
}

# File: src/main/resources/application.properties
logging.file.name=app.log

Need a hint?

Use SLF4J Logger to add a log message. Also print to console to see immediate output.

4

Run and verify log output

Run the Spring Boot application. Then open the app.log file in the project root folder and verify it contains the line with "Application started" logged by the logger.

Spring Boot

package com.example.logging;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@SpringBootApplication
public class LoggingApplication {
    private static final Logger logger = LoggerFactory.getLogger(LoggingApplication.class);

    public static void main(String[] args) {
        SpringApplication.run(LoggingApplication.class, args);
        System.out.println("Application started");
        logger.info("Application started");
    }
}

# File: src/main/resources/application.properties
logging.file.name=app.log

# Run the application and check app.log for the log message
# Your code here

Need a hint?

Run the app using your IDE or command line. Then open app.log to see the logged message.