Why Not System.out.println() for Logging
Fast recall
Quick revision
Core answer
System.out.println writes plain text to standard output. It has no logging level, logger name, parameterized event, exception field, MDC context, or runtime filtering of its own. A logging API such as SLF4J, together with a configured provider, supplies those features and can still write to stdout for container collection. The problem is not stdout itself; it is using an unstructured print call as the application's logging model.
Interview-ready guide
Interview answer
System.out.println is a print call, not a production logging model. It writes a plain string to stdout and has no event level, logger name, parameter binding, throwable field, MDC context, or runtime filtering of its own. A platform may capture stdout, so I would not say that stdout always disappears. Instead, I use SLF4J with a configured provider because it creates meaningful events and lets each environment control thresholds, format, and routing without changing application code. The provider can still write those events to stdout in a container. I also use parameterized messages and pass exceptions as exceptions, while keeping secrets out of every output.
Why Not System.out.println() for Logging
Direct Answer
System.out.println writes plain text to standard output. It has no logging level, logger name, parameterized event, exception field, MDC context, or runtime filtering of its own. A logging API such as SLF4J, together with a configured provider, supplies those features and can still write to stdout for container collection. The problem is not stdout itself; it is using an unstructured print call as the application's logging model.
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Answer these without looking back at the article.
- What is the default logging framework used in Spring Boot?
- How would you change the log level of a package at runtime in Spring Boot?
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