Package-level log configuration in Spring Boot - Mini Project: Build & Apply

Package-level log configuration in Spring Boot

📖 Scenario: You are building a Spring Boot application that has multiple packages. You want to control the logging level separately for each package to help with debugging and monitoring.

🎯 Goal: Configure logging levels at the package level in a Spring Boot application using application.properties file.

📋 What You'll Learn

Create a Spring Boot project with at least two packages: com.example.service and com.example.controller

Set the logging level for com.example.service to DEBUG

Set the logging level for com.example.controller to INFO

Verify that the logging configuration is correctly applied

💡 Why This Matters

🌍 Real World

In real projects, controlling logging levels per package helps developers focus on relevant logs and reduces noise during debugging and monitoring.

💼 Career

Understanding package-level logging configuration is essential for backend developers working with Spring Boot to maintain and troubleshoot applications efficiently.

1

Create packages in the Spring Boot project

Create two packages in your Spring Boot project: com.example.service and com.example.controller. You do not need to add any classes yet.

Spring Boot

# Create packages com.example.service and com.example.controller
# Your code here

Hint

In your IDE or project structure, create the two packages exactly as com.example.service and com.example.controller.

2

Add logging level configuration in application.properties

In the src/main/resources/application.properties file, add two lines to set the logging level for com.example.service to DEBUG and for com.example.controller to INFO.

Spring Boot

# Packages created: com.example.service and com.example.controller
# No classes needed yet

# Add logging level configuration below
# Your code here

Hint

Open application.properties and add these exact lines:

logging.level.com.example.service=DEBUG
logging.level.com.example.controller=INFO

3

Add simple classes to each package with logging

Create a class ServiceClass in com.example.service and a class ControllerClass in com.example.controller. In each class, add a logger and a method that logs a message at the DEBUG level for ServiceClass and at the INFO level for ControllerClass.

Spring Boot

# Packages created: com.example.service and com.example.controller
# No classes needed yet

# src/main/resources/application.properties
logging.level.com.example.service=DEBUG
logging.level.com.example.controller=INFO

// Create ServiceClass and ControllerClass with logging
// Your code here

Hint

Create two classes with the exact names and add logging using LoggerFactory.getLogger. Use logger.debug in ServiceClass and logger.info in ControllerClass.

4

Complete the Spring Boot application with main class and run

Add the main Spring Boot application class Application in com.example package. In the main method, create instances of ServiceClass and ControllerClass and call their logging methods. This completes the package-level log configuration setup.

Spring Boot

package com.example.service;

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

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

    public void logDebug() {
        logger.debug("This is a DEBUG message from ServiceClass");
    }
}

package com.example.controller;

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

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

    public void logInfo() {
        logger.info("This is an INFO message from ControllerClass");
    }
}

# src/main/resources/application.properties
logging.level.com.example.service=DEBUG
logging.level.com.example.controller=INFO

// Add main Application class and call logging methods
// Your code here

Hint

Create a Application class annotated with @SpringBootApplication. In main, run the app and call the logging methods on instances of ServiceClass and ControllerClass.

Practice

1. What is the purpose of setting logging.level.<package>=<level> in Spring Boot's application.properties?

easy

A. To control the logging detail for a specific Java package

B. To define the database connection URL

C. To set the server port number

D. To configure the application's timezone

Solution

1. Step 1: Understand the configuration key

   The key logging.level.<package> is used to specify logging levels for Java packages in Spring Boot.

2. Step 2: Identify the purpose of this setting

   This setting controls how detailed the logs are for that package, helping to focus on important logs and reduce noise.

3. Final Answer:

   To control the logging detail for a specific Java package -> Option A

4. Quick Check:

   Package-level log control = A [OK]

Hint: Remember: logging.level.package sets log detail per package [OK]

Common Mistakes:

• Confusing logging level with server or database settings
• Trying to set logging level without specifying a package
• Using incorrect property keys like logging.package.level

2. Which of the following is the correct syntax to set the log level to DEBUG for the package com.example.service in application.properties?

easy

A. logging.level=com.example.service=DEBUG

B. log.level.com.example.service=DEBUG

C. logging.com.example.service.level=DEBUG

D. logging.level.com.example.service=DEBUG

Solution

1. Step 1: Recall the correct property format

   The correct format is logging.level.<package>=<level>, so the package name comes immediately after logging.level..

2. Step 2: Match the option to the format

   logging.level.com.example.service=DEBUG matches this format exactly: logging.level.com.example.service=DEBUG.

3. Final Answer:

   logging.level.com.example.service=DEBUG -> Option D

4. Quick Check:

   Correct syntax = B [OK]

Hint: Use logging.level.package=LEVEL exactly as shown [OK]

Common Mistakes:

• Adding extra '=' signs in the property
• Swapping order of package and level
• Using 'log.level' instead of 'logging.level'

3. Given the following application.properties settings:
logging.level.com.example=INFO
logging.level.com.example.service=DEBUG
What will be the log level for classes in com.example.service package?

medium

A. INFO

B. DEBUG

C. ERROR

D. WARN

Solution

1. Step 1: Understand package-level log hierarchy

   More specific package settings override broader ones. Here, com.example.service is more specific than com.example.

2. Step 2: Determine effective log level

   The com.example.service package is set to DEBUG, which overrides the INFO level set for com.example.

3. Final Answer:

   DEBUG -> Option B

4. Quick Check:

   Specific package level overrides general = C [OK]

Hint: More specific package log level overrides parent package [OK]

Common Mistakes:

• Assuming parent package level applies to all subpackages
• Ignoring more specific package settings
• Confusing INFO and DEBUG levels

4. You set logging.level.com.example=TRACE in application.properties but still see only INFO logs from com.example classes. What is the most likely cause?

medium

A. Logging is disabled globally

B. TRACE level is not supported in Spring Boot

C. Another configuration overrides the log level to INFO

D. The package name is misspelled in the properties file

Solution

1. Step 1: Verify if TRACE is supported

   TRACE is a valid log level in Spring Boot, so this is not the issue.

2. Step 2: Consider configuration overrides

   If logs show INFO instead of TRACE, likely another config (like environment variables or YAML) overrides the level to INFO.

3. Final Answer:

   Another configuration overrides the log level to INFO -> Option C

4. Quick Check:

   Config override causes unexpected log level = D [OK]

Hint: Check for conflicting configs if log level seems ignored [OK]

Common Mistakes:

• Assuming TRACE is unsupported
• Not checking for typos in package name
• Ignoring global logging settings

5. You want to reduce log noise by setting ERROR level for com.example.repository but keep DEBUG for com.example.service. Which application.properties configuration achieves this?

hard

A. logging.level.com.example.repository=ERROR
logging.level.com.example.service=DEBUG

B. logging.level.com.example=ERROR
logging.level.com.example.service=DEBUG

C. logging.level.com.example.repository=DEBUG
logging.level.com.example.service=ERROR

D. logging.level.com.example.repository=INFO
logging.level.com.example.service=DEBUG

Solution

1. Step 1: Set ERROR level specifically for repository package

   Use logging.level.com.example.repository=ERROR to reduce noise from repository logs.

2. Step 2: Set DEBUG level specifically for service package

   Use logging.level.com.example.service=DEBUG to keep detailed logs for service package.

3. Step 3: Combine both settings correctly

   logging.level.com.example.repository=ERROR logging.level.com.example.service=DEBUG correctly sets both packages with their respective levels in application.properties.

4. Final Answer:

   logging.level.com.example.repository=ERROR logging.level.com.example.service=DEBUG -> Option A

5. Quick Check:

   Separate package levels set correctly = A [OK]

Hint: Set each package level separately for precise control [OK]

Common Mistakes:

• Setting parent package level instead of specific packages
• Swapping log levels between packages
• Using incorrect property keys or syntax