Log levels (TRACE, DEBUG, INFO, WARN, ERROR) in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What log messages appear at INFO level?

Given the Spring Boot application configured with log level INFO, which log messages will be printed to the console?

Spring Boot

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

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

    public static void main(String[] args) {
        logger.trace("Trace message");
        logger.debug("Debug message");
        logger.info("Info message");
        logger.warn("Warn message");
        logger.error("Error message");
    }
}

A Only 'Error message' is printed.

B Only 'Info message', 'Warn message', and 'Error message' are printed.

C All messages from 'Trace message' to 'Error message' are printed.

D Only 'Warn message' and 'Error message' are printed.

💡 Hint

INFO level shows messages at INFO and above severity.

At INFO level, messages logged at INFO, WARN, and ERROR levels are shown. TRACE and DEBUG are lower levels and are not printed.

📝 Syntax

intermediate

Which log level setting disables all logging?

In Spring Boot's application.properties, which log level setting disables all logging output?

A logging.level.root=OFF

B logging.level.root=ERROR

C logging.level.root=DISABLE

D logging.level.root=NONE

💡 Hint

Check the official log level names for disabling logs.

The OFF level disables all logging. NONE and DISABLE are not valid log levels. ERROR still allows error logs.

🔧 Debug

advanced

Why does DEBUG log not appear despite setting DEBUG level?

A developer sets logging.level.com.example=DEBUG in application.properties but DEBUG messages from com.example.service.MyService do not appear. What is the most likely cause?

A The root log level is set to ERROR, which overrides package settings.

B The application.properties file is not loaded at runtime.

C The logging framework does not support DEBUG level.

D The logger in MyService is using a different package name than com.example.service.

💡 Hint

Check the exact package name used in the logger declaration.

Log level settings apply to package names. If the logger uses a different package or class name, the setting won't apply.

🧠 Conceptual

advanced

What is the order of log levels from most to least detailed?

Arrange the log levels from the most detailed (shows most messages) to the least detailed (shows fewest messages).

A 1,2,3,4,5

B 5,4,3,2,1

C 3,2,1,4,5

D 2,1,3,4,5

💡 Hint

TRACE logs everything, ERROR logs only errors.

TRACE is the most detailed, followed by DEBUG, INFO, WARN, and ERROR as the least detailed.

❓ state_output

expert

What is the output count of WARN and ERROR logs with mixed package levels?

Given these log level settings in application.properties: logging.level.com.example=DEBUG logging.level.com.example.service=ERROR And this code: import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class MyService { private static final Logger logger = LoggerFactory.getLogger(MyService.class); public void run() { logger.debug("Debug message"); logger.info("Info message"); logger.warn("Warn message"); logger.error("Error message"); } } How many log messages will be printed when run() is called?

A 'Debug', 'Info', 'Warn', and 'Error' messages are printed (4 messages).

B 'Warn message' and 'Error message' are printed (2 messages).

C Only 'Error message' is printed (1 message).

D 'Info', 'Warn', and 'Error' messages are printed (3 messages).

💡 Hint

More specific package settings override broader ones.

The com.example.service package is set to ERROR level, so only ERROR messages print from MyService. The DEBUG level on com.example does not apply here.