Spring Boot Logging

External

SpringBoot Documentation - Logging

Internal

• Spring Boot Concepts
• Spring Logging

Overview

By default, a Spring Boot application that uses starters has a Logback log runtime: logback-classic-....jar is present in the application JAR. Logging is configured by default to write to the console at INFO level. log4j support is also available (log4j-api-2.11.1.jar, log4j-to-slf4j-2.11.1.jar). The following statements will generate INFO logs at the console without any additional configuration:

@Slf4j
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
        log.info("in main()");
        ...
    }
}

The default log output includes:

• Date and time with millisecond precision.
• Log level (ERROR, WARN, INFO, DEBUG or TRACE).
• Process ID
• A "---" separator.
• The thread name enclosed in square brackets and possibly truncated.
• The logger name, possibly abbreviated.
• The log message.

The default log configuration sends ERROR/WARN/INFO log messages to the console (standard out). DEBUG for core loggers (the container, Hibernate and Spring Boot) can be enabled globally for the application by specifying --debug on command line:

java -jar app.jar --debug

Alternatively:

debug: true

can be set in application.yml/application.properties. This generates a large quantity of logging, but it does not enable application-level DEBUG logging. If you need that, it will have to be configured specifically as shown below.

Similar to --debug, --trace can also be enabled.

application.yml Logging Configuration

Basic logging configuration can be applied directly in application.yml/application.properties. Root logging level can be controlled as such:

logging:
  level:
    root: WARN

Logger Level Configuration

Individual loggers can be configured with entries prefixed by "logging.level", followed by the name of the logger:

logging:
  level:
    playground:
      example: DEBUG

Optionally, the long logger names can be collapsed on a single line, as follows. The above is equivalent with:

logging:
  level:
    playground.example: DEBUG

Setting a logging level on a specific logger configuration applies the same logging level on all logger subpackages.

File Output Configuration

logging:
  path: /var/log/
  file: my-file.log

More details about file output configuration can be found here: Spring Boot Logging - File Output.

logback.xml Logging Configuration

Better control over logging levels and format can be obtained by placing a Logback configuration file logback.xml in src/main/resources. This is an example of a simple logback.xml that will work:

<configuration>
  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
    <encoder>
      <pattern>
        %d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
      </pattern>
    </encoder>
  </appender>
  <logger name="root" level="INFO"/>
  <root level="INFO">
    <appender-ref ref="STDOUT" />
  </root>
</configuration>

Note that the default log formatting uses a fancier, color format, and the above configuration will overwrite the default log formatting.

If the same logger is configured both in application.yml and in logback.xml, application.yml configuration takes precendenc.