Package-level log configuration in Spring Boot - Step-by-Step Execution

Concept Flow - Package-level log configuration

Start Application

↓

Load application.properties

↓

Read logging.level.package=value

↓

Set log level for package

↓

Run application code

↓

Log messages filtered by package log level

↓

Output logs accordingly

Spring Boot reads the logging level set for a package from configuration and applies it to filter log messages during runtime.

Execution Sample

Spring Boot

logging.level.com.example.service=DEBUG

// In code:
logger.debug("Debug message");
logger.info("Info message");

Sets DEBUG level logging for 'com.example.service' package, so debug and higher messages appear.

Execution Table

Step	Action	Package Log Level	Log Message	Message Level	Output?
1	Start application	default INFO	-	-	No output
2	Load config: logging.level.com.example.service=DEBUG	com.example.service=DEBUG	-	-	No output
3	Run code in com.example.service	DEBUG	Debug message	DEBUG	Yes
4	Run code in com.example.service	DEBUG	Info message	INFO	Yes
5	Run code in com.example.other	INFO (default)	Debug message	DEBUG	No
6	Run code in com.example.other	INFO (default)	Info message	INFO	Yes
7	End of execution	-	-	-	Stop logging

💡 Application finishes running; logging stops.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 6	Final
packageLogLevel['com.example.service']	INFO (default)	DEBUG	DEBUG	DEBUG	DEBUG
packageLogLevel['com.example.other']	INFO (default)	INFO (default)	INFO (default)	INFO (default)	INFO (default)

Key Moments - 2 Insights

Why does a DEBUG log message in 'com.example.other' package not appear?

Because 'com.example.other' uses the default INFO level, which filters out DEBUG messages as shown in execution_table row 5.

How does Spring Boot know which log level to apply to a package?

It reads the 'logging.level.<package>' property from configuration before running code, as seen in step 2 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution table, what is the log level for 'com.example.service' after loading configuration?

A ERROR

B INFO

C DEBUG

D WARN

💡 Hint

Check Step 2 in the execution_table where config is loaded.

At which step does a DEBUG message from 'com.example.other' get filtered out?

A Step 5

B Step 3

C Step 4

D Step 6

💡 Hint

Look at Step 5 in the execution_table for 'com.example.other' package.

If we set 'logging.level.com.example.other=DEBUG', what changes in the execution table?

A Step 6 output changes to No

B Step 5 output changes to Yes

C Step 3 output changes to No

D No changes

💡 Hint

Refer to variable_tracker and Step 5 output behavior.

Concept Snapshot

Package-level log configuration in Spring Boot:
- Set log level per package in application.properties using 'logging.level.<package>=LEVEL'
- Levels: TRACE < DEBUG < INFO < WARN < ERROR
- Messages below set level are filtered out
- Helps focus logs on specific parts of app
- Default level is INFO if not set

Full Transcript

This visual execution shows how Spring Boot applies package-level log configuration. When the application starts, it loads the logging.level properties from application.properties. For example, setting logging.level.com.example.service=DEBUG means all debug and higher messages in that package will be logged. The execution table traces steps where messages are logged or filtered based on package log levels. Variables track the current log level per package. Key moments clarify why some messages appear or not. The quiz tests understanding of how configuration affects logging output.