Customizing your log output format in Spring Boot applications is essential for clear and efficient debugging. By tailoring the way logs are displayed, you can highlight the most relevant information, reduce noise, and make it easier to trace issues as they arise. Well-structured logs help you quickly identify problems, monitor application behavior, and improve overall maintainability. In this chapter, you will learn how to adjust log formats to suit your specific needs, making your logs both more readable and more useful for troubleshooting.

Customizing Log Output Format in Spring Boot

You can control how your logs look in Spring Boot by changing the log output format. This helps you include the right information, make logs easier to read, and match your team's standards.

Log Pattern and Layout

The log pattern defines the structure and order of information in each log line. In Spring Boot, you set the log pattern in the application.properties or application.yml file. Use the logging.pattern.console property for console output, or logging.pattern.file for file output.

Example:

logging.pattern.console=%d{yyyy-MM-dd HH:mm:ss} %-5level %logger{36} - %msg%n

This pattern means:

• %d{yyyy-MM-dd HH:mm:ss}: Timestamp in year-month-day hour:minute:second format;
• %-5level: Log level (like INFO, WARN, ERROR), padded for alignment;
• %logger{36}: Logger name, up to 36 characters;
• %msg: The actual log message;
• %n: New line at the end of the log entry.

Customizing Timestamp

You can change the timestamp format by editing the %d{} part of the pattern. For example, %d{HH:mm:ss.SSS} shows only time with milliseconds.

Adding More Information

You can include other details in your log pattern:

• %thread: Thread name running the log statement;
• %M: Method name;
• %line: Line number in the source code;
• %X{key}: Custom values from the MDC (Mapped Diagnostic Context).

Example with more details:

logging.pattern.console=%d{HH:mm:ss} [%thread] %-5level %logger{36} - %msg%n

Using YAML Configuration

If you use YAML, the setup looks like this:

logging:
  pattern:
    console: "%d{yyyy-MM-dd HH:mm:ss} %-5level %logger{36} - %msg%n"

Summary

• Change log output format with logging.pattern.console or logging.pattern.file;
• Adjust the pattern to include the timestamp, log level, logger, thread, or other details;
• Use clear, consistent patterns to make logs easier to read and analyze.