SLF4J and Logback basics in Spring Boot - Mini Project: Build & Apply

SLF4J and Logback Basics in Spring Boot

📖 Scenario: You are building a simple Spring Boot application that needs to log messages for monitoring and debugging. You will set up SLF4J with Logback, the default logging framework in Spring Boot, to log messages at different levels.

🎯 Goal: Learn how to create a logger using SLF4J, configure Logback with a simple XML file, and log messages at INFO and ERROR levels in a Spring Boot application.

📋 What You'll Learn

Create a Spring Boot application class

Create a logger instance using SLF4J LoggerFactory

Configure Logback with a basic logback.xml file

Log messages at INFO and ERROR levels in the application

💡 Why This Matters

🌍 Real World

Logging is essential in real applications to track what the app is doing and find problems quickly.

💼 Career

Understanding SLF4J and Logback is important for Java developers working with Spring Boot to maintain and debug applications.

1

Create Spring Boot Application Class with Logger

Create a Spring Boot application class named LoggingDemoApplication in package com.example.logging. Inside it, create a private static final logger called logger using LoggerFactory.getLogger(LoggingDemoApplication.class).

Spring Boot

package com.example.logging;

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

@SpringBootApplication
public class LoggingDemoApplication {
    // Create logger here
}

Need a hint?

Use LoggerFactory.getLogger(LoggingDemoApplication.class) to create the logger.

2

Add Basic Logback Configuration File

Create a logback.xml file in src/main/resources folder. Add a configuration root element with a console appender named STDOUT that outputs logs to the console with pattern %d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n. Set the root logger level to INFO and attach the STDOUT appender.

Spring Boot

package com.example.logging;

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

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

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

Need a hint?

Use a ConsoleAppender with the specified pattern and set root level to INFO.

3

Log INFO and ERROR Messages in main Method

Inside the main method of LoggingDemoApplication, after starting the application, add a log message at INFO level with text "Application started successfully" and a log message at ERROR level with text "An error occurred during startup".

Spring Boot

package com.example.logging;

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

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

    public static void main(String[] args) {
        SpringApplication.run(LoggingDemoApplication.class, args);
        // Add INFO and ERROR log messages here
    }
}

/* logback.xml content in src/main/resources:

  
    
      %d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
    
  

  
    
  

*/

Need a hint?

Use logger.info() and logger.error() with the exact messages.

4

Add Spring Boot Starter Logging Dependency

In your pom.xml file, ensure you have the dependency spring-boot-starter-logging included. Add the following dependency inside <dependencies>: <dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-logging</artifactId></dependency>

Spring Boot

 in pom.xml -->

Need a hint?

This dependency is included by default in Spring Boot starter projects but add it explicitly if missing.