Log levels (TRACE, DEBUG, INFO, WARN, ERROR) in Spring Boot - Step-by-Step Execution

Concept Flow - Log levels (TRACE, DEBUG, INFO, WARN, ERROR)

Start Application

↓

Log Event Occurs

↓

Check Log Level Setting

↓

Is Event Level >= Configured Level?

No→Skip Log

↓

Write Log Message

↓

Continue Application Execution

The application checks if the event's log level meets or exceeds the configured level. If yes, it writes the log message; otherwise, it skips logging.

Execution Sample

Spring Boot

logger.trace("Trace message");
logger.debug("Debug message");
logger.info("Info message");
logger.warn("Warn message");
logger.error("Error message");

Logs messages at different levels; only messages at or above the configured level are output.

Execution Table

Step	Log Call	Configured Level	Is Log Level >= Configured?	Action	Output
1	TRACE	INFO	No	Skip Log	No output
2	DEBUG	INFO	No	Skip Log	No output
3	INFO	INFO	Yes	Write Log	Info message
4	WARN	INFO	Yes	Write Log	Warn message
5	ERROR	INFO	Yes	Write Log	Error message
6	-	-	-	-	End of logging calls

💡 Logging stops after all log calls are checked against the configured level.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
Configured Level	INFO	INFO	INFO	INFO	INFO	INFO	INFO
Current Log Call	-	TRACE	DEBUG	INFO	WARN	ERROR	-
Log Output	[]	[]	[]	["Info message"]	["Info message", "Warn message"]	["Info message", "Warn message", "Error message"]	["Info message", "Warn message", "Error message"]

Key Moments - 2 Insights

Why are TRACE and DEBUG messages not shown when the configured level is INFO?

Because TRACE and DEBUG are lower priority than INFO, the check in the execution_table rows 1 and 2 shows 'No' for 'Is Log Level >= Configured?', so these messages are skipped.

What happens if the configured level is set to ERROR?

Only ERROR messages will be logged because all other levels are lower priority. This is similar to the logic in the execution_table but with a higher configured level, causing more skips.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output after step 3?

A ["Debug message"]

B ["Info message"]

C []

D ["Trace message"]

💡 Hint

Check the 'Output' column at step 3 in the execution_table.

At which step does the log level first meet the configured level?

A Step 3

B Step 2

C Step 1

D Step 5

💡 Hint

Look at the 'Is Log Level >= Configured?' column in the execution_table.

If the configured level changes to DEBUG, which log calls will be output?

A INFO, WARN, ERROR

B TRACE, DEBUG, INFO, WARN, ERROR

C DEBUG, INFO, WARN, ERROR

D WARN, ERROR

💡 Hint

Compare the configured level in variable_tracker and think which levels are >= DEBUG.

Concept Snapshot

Log levels control which messages are recorded.
Levels in order: TRACE < DEBUG < INFO < WARN < ERROR.
Only messages at or above the configured level are logged.
Lower levels are skipped to reduce noise.
Configure level to control log detail and performance.

Full Transcript

In Spring Boot, log levels determine which messages are recorded. When the application runs, each log call is checked against the configured log level. If the message's level is equal or higher priority than the configured level, it is logged; otherwise, it is skipped. For example, if the configured level is INFO, TRACE and DEBUG messages are ignored, but INFO, WARN, and ERROR messages are shown. This helps control how much detail appears in logs, balancing information and noise. Changing the configured level changes which messages appear.