Log Format

The default log output from Spring Boot resembles the following example:

2023-04-27T19:52:05.903Z  INFO 2954 --- [           main] o.s.b.d.f.s.MyApplication                : Starting MyApplication using Java 17.0.6 with PID 2954 (/opt/apps/myapp.jar started by myuser in /opt/apps/)
2023-04-27T19:52:05.922Z  INFO 2954 --- [           main] o.s.b.d.f.s.MyApplication                : No active profile set, falling back to 1 default profile: "default"
2023-04-27T19:52:08.014Z  INFO 2954 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2023-04-27T19:52:08.040Z  INFO 2954 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2023-04-27T19:52:08.042Z  INFO 2954 --- [           main] o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/10.1.5]
2023-04-27T19:52:08.306Z  INFO 2954 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2023-04-27T19:52:08.313Z  INFO 2954 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 2264 ms
2023-04-27T19:52:09.228Z  INFO 2954 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2023-04-27T19:52:09.247Z  INFO 2954 --- [           main] o.s.b.d.f.s.MyApplication                : Started MyApplication in 4.573 seconds (process running for 5.541)

The following items are output:

  • Date and Time: Millisecond precision and easily sortable.

  • Log Level: ERROR, WARN, INFO, DEBUG, or TRACE.

  • Process ID.

  • A --- separator to distinguish the start of actual log messages.

  • Thread name: Enclosed in square brackets (may be truncated for console output).

  • Logger name: This is usually the source class name (often abbreviated).

  • The log message.

Logback does not have a FATAL level. It is mapped to ERROR.