File-based logging in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Log file creation with default Spring Boot logging

You run a Spring Boot application without any custom logging configuration. Which file will be created by default to store logs?

A No log file is created by default; logs go to console only

B application.log in the current directory

C logs/app.log inside a logs folder

D spring.log in the current directory

💡 Hint

Think about what Spring Boot does if you don't specify any logging file path.

By default, Spring Boot logs only to the console unless you configure a file appender. No log file is created automatically.

❓ Configuration

intermediate

Configuring log file location in application.properties

Which property correctly configures Spring Boot to write logs to a file named 'myapp.log' in the 'logs' folder?

A logging.file=logs/myapp.log

B logging.path=logs/myapp.log

C logging.file.path=logs/myapp.log

D logging.file.name=logs/myapp.log

💡 Hint

Check the exact property name for specifying the log file name.

The property 'logging.file.name' sets the full path and filename for the log file. 'logging.file.path' sets only the directory.

❓ Troubleshoot

advanced

Log file not created despite configuration

You set 'logging.file.name=logs/app.log' in application.properties, but no log file appears after running the app. What is the most likely cause?

A The log level is set to ERROR, so no logs are written

B The 'logs' directory does not exist and Spring Boot does not create it automatically

C The application.properties file is not in the classpath

D Spring Boot requires a separate logging framework dependency to write files

💡 Hint

Think about folder creation behavior for log files.

Spring Boot does not create missing directories for log files automatically. The 'logs' folder must exist before running the app.

🔀 Workflow

advanced

Steps to enable rolling log files in Spring Boot

What is the correct order of steps to configure rolling log files using Logback in Spring Boot?

A 1,3,2,4

B 2,1,3,4

C 1,2,3,4

D 3,1,2,4

💡 Hint

Think about creating config, defining appender, linking it, then restarting.

First create the config file, then define the appender, link it to the logger, and finally restart the app to apply.

✅ Best Practice

expert

Best practice for sensitive data in log files

Which approach is best to avoid logging sensitive information like passwords in Spring Boot file logs?

A Use a custom log filter to mask or remove sensitive data before writing logs

B Set logging.level.root=OFF to disable all logging

C Write sensitive data only to console logs, not files

D Encrypt the entire log file after application shutdown

💡 Hint

Think about controlling what gets logged rather than disabling logging.

A custom log filter can selectively mask or remove sensitive data, keeping logs useful and secure.

Practice

1. What is the main purpose of file-based logging in a Spring Boot application?

easy

A. To save application messages to a file for later review

B. To send application messages only to the console

C. To delete old log files automatically

D. To encrypt application data before saving

Solution

1. Step 1: Understand logging basics in Spring Boot

   Logging captures messages about app behavior. File-based logging stores these messages in a file.

2. Step 2: Identify the purpose of file-based logging

   It allows reviewing logs later for debugging or monitoring, unlike console-only logging.

3. Final Answer:

   To save application messages to a file for later review -> Option A

4. Quick Check:

   File-based logging = save logs to file [OK]

Hint: File-based logging means saving logs to a file [OK]

Common Mistakes:

• Confusing file logging with console logging
• Thinking it deletes old logs automatically
• Assuming it encrypts logs by default

2. Which of the following is the correct way to enable file-based logging in application.properties?

easy

A. logging.filepath=logs/app.log

B. logging.file.name=logs/app.log

C. log.file=logs/app.log

D. logging.pathfile=logs/app.log

Solution

1. Step 1: Recall Spring Boot logging property names

   The correct property to set the log file name is logging.file.name.

2. Step 2: Check each option for correctness

   Only logging.file.name=logs/app.log uses the exact property logging.file.name with a valid file path.

3. Final Answer:

   logging.file.name=logs/app.log -> Option B

4. Quick Check:

   Correct property for log file name = logging.file.name [OK]

Hint: Use logging.file.name to set log file path [OK]

Common Mistakes:

• Using incorrect property names like logging.filepath
• Misspelling property keys
• Confusing logging.file.name with logging.pathfile

3. Given this application.yml snippet:

logging:
  file:
    name: logs/myapp.log
  level:
    root: INFO

What will happen when the Spring Boot app runs?

medium

A. Logs will only print to console with DEBUG level

B. Application will fail to start due to syntax error

C. Logs will be saved to logs/myapp.log but only ERROR level

D. Logs will be saved to logs/myapp.log with INFO level and above

Solution

1. Step 1: Analyze logging.file.name setting

   The logs will be saved to the file path logs/myapp.log as configured.

2. Step 2: Analyze logging.level.root setting

   The root log level is INFO, so logs INFO and above will be recorded.

3. Final Answer:

   Logs will be saved to logs/myapp.log with INFO level and above -> Option D

4. Quick Check:

   File path + INFO level = logs/myapp.log with INFO+ logs [OK]

Hint: logging.file.name sets file, logging.level.root sets minimum log level [OK]

Common Mistakes:

• Assuming logs only go to console
• Confusing log level INFO with DEBUG or ERROR
• Thinking YAML syntax is invalid here

4. You configured file logging in application.properties as:
logging.file.name=logs/app.log
But no log file is created after running the app. What is the most likely cause?

medium

A. The property should be logging.file.path, not logging.file.name

B. The log level is set to OFF by default

C. The logs directory does not exist and is not created automatically

D. Spring Boot does not support file logging

Solution

1. Step 1: Check directory existence for log file

   If the logs directory does not exist, Spring Boot may not create it automatically, so no file is created.

2. Step 2: Verify other options

   Log level defaults to INFO, property name is correct, and Spring Boot supports file logging.

3. Final Answer:

   The logs directory does not exist and is not created automatically -> Option C

4. Quick Check:

   Missing log directory = no log file created [OK]

Hint: Ensure log directory exists before running app [OK]

Common Mistakes:

• Using wrong property name
• Assuming Spring Boot disables file logging
• Ignoring missing directory errors

5. You want to keep log files organized by date in Spring Boot. Which configuration snippet in application.yml correctly enables daily rolling log files using Logback?

hard

A. logging:
file:
name: logs/app.log
logback:
rollingpolicy:
file-name-pattern: logs/app-%d{yyyy-MM-dd}.log

B. logging:
file:
name: logs/app.log
logback:
rollingPolicy:
filePattern: logs/app-%d{yyyy-MM-dd}.log

C. logging:
file:
name: logs/app.log
logback:
rollingpolicy:
fileNamePattern: logs/app-%d{yyyy-MM-dd}.log

D. logging:
file:
path: logs
logback:
rollingPolicy:
fileNamePattern: logs/app-%d{yyyy-MM-dd}.log

Solution

1. Step 1: Identify correct property names for Logback rolling policy

   The correct key is rollingpolicy (lowercase 'p'), and file-name-pattern (kebab-case) is the correct pattern key.

2. Step 2: Check each option for exact spelling and structure

   logging: file: name: logs/app.log logback: rollingpolicy: file-name-pattern: logs/app-%d{yyyy-MM-dd}.log uses correct keys: rollingpolicy and file-name-pattern.

3. Final Answer:

   logging: file: name: logs/app.log logback: rollingpolicy: file-name-pattern: logs/app-%d{yyyy-MM-dd}.log -> Option A

4. Quick Check:

   Correct keys for rollingpolicy = logging: file: name: logs/app.log logback: rollingpolicy: file-name-pattern: logs/app-%d{yyyy-MM-dd}.log [OK]

Hint: Use exact keys: rollingpolicy and file-name-pattern [OK]

Common Mistakes:

• Using uppercase 'rollingPolicy' instead of 'rollingpolicy'
• Using 'filePattern' or 'fileNamePattern' instead of 'file-name-pattern'
• Confusing logging.file.name with logging.file.path