Logger creation in classes in Spring Boot - Step-by-Step Execution

Concept Flow - Logger creation in classes

Start Class

↓

Declare Logger

↓

Initialize Logger with LoggerFactory

↓

Use Logger in Methods

↓

Log Messages at Different Levels

↓

End Class

This flow shows how a logger is declared, initialized, and used inside a Spring Boot class to log messages.

Execution Sample

Spring Boot

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class MyService {
  private static final Logger logger = LoggerFactory.getLogger(MyService.class);

  public void doWork() {
    logger.info("Work started");
  }
}

This code creates a logger in a Spring Boot class and logs an info message inside a method.

Execution Table

Step	Action	Evaluation	Result
1	Class MyService loaded	Class loaded	Ready to declare logger
2	Declare logger variable	private static final Logger logger	Logger variable declared but not initialized
3	Initialize logger with LoggerFactory.getLogger(MyService.class)	LoggerFactory creates logger instance	Logger instance assigned to logger variable
4	Call doWork() method	Method invoked	Inside method body
5	Execute logger.info("Work started")	Log message at INFO level	Message sent to logging system
6	Method doWork() ends	No return value	Method completes
7	Class usage ends	No further actions	Program continues or ends

💡 Logging completes after method execution; no more code to run in this example.

Variable Tracker

Variable	Start	After Initialization	After Method Call	Final
logger	null	Logger instance for MyService	Logger instance for MyService	Logger instance for MyService

Key Moments - 3 Insights

Why do we use LoggerFactory.getLogger(MyService.class) instead of creating Logger directly?

LoggerFactory.getLogger(MyService.class) creates a logger tied to the class name, which helps identify log messages' source. This is shown in execution_table step 3 where the logger instance is created.

Why is the logger declared as static and final?

Declaring logger as static means one shared instance per class, and final means it cannot be reassigned. This is important for efficiency and consistency, as seen in execution_table step 2.

What happens when logger.info() is called inside the method?

The log message is sent to the logging system at INFO level, which can be seen in execution_table step 5 where the message is processed.

Visual Quiz - 3 Questions

Look at the execution table, what is the state of the logger variable after step 3?

A It holds a Logger instance for MyService

B It holds a String message

C It is null

D It is uninitialized

💡 Hint

Check the 'Result' column in step 3 of the execution_table.

At which step does the log message "Work started" get sent to the logging system?

A Step 3

B Step 5

C Step 2

D Step 6

💡 Hint

Look for the step where logger.info() is executed in the execution_table.

If the logger was not declared static, what would change in the variable_tracker?

A Logger would remain null

B Logger would be shared across all classes

C Logger would be initialized multiple times per instance

D Logger would be a local variable

💡 Hint

Consider how static affects variable initialization shown in variable_tracker.

Concept Snapshot

Logger creation in Spring Boot classes:
- Declare logger as private static final
- Initialize with LoggerFactory.getLogger(ClassName.class)
- Use logger methods (info, debug, error) inside class methods
- Static ensures one logger per class
- Logger helps track runtime events clearly

Full Transcript

In Spring Boot, to create a logger inside a class, you declare a private static final Logger variable. You initialize it using LoggerFactory.getLogger with the class name. This ties the logger to the class, making log messages easy to identify. Inside your methods, you call logger methods like info() to send messages to the logging system. The static keyword means only one logger instance exists per class, improving efficiency. This process helps track what your application is doing while it runs.