Spring Boot uses Commons Logging for all internal logging, but leaves the underlying log implementation open. Default configurations are provided for Java Util Logging, Log4J, Log4J2 and Logback. In each case loggers are pre-configured to use console output with optional file output also available.
By default, If you use the ‘Starter POMs’, Logback will be used for logging. Appropriate Logback routing is also included to ensure that dependent libraries that use Java Util Logging, Commons Logging, Log4J or SLF4J will all work correctly.
Tip | |
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There are a lot of logging frameworks available for Java. Don’t worry if the above list seems confusing. Generally you won’t need to change your logging dependencies and the Spring Boot defaults will work just fine. |
The default log output from Spring Boot looks like this:
2014-03-05 10:57:51.112 INFO 45469 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/7.0.52 2014-03-05 10:57:51.253 INFO 45469 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2014-03-05 10:57:51.253 INFO 45469 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1358 ms 2014-03-05 10:57:51.698 INFO 45469 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean : Mapping servlet: 'dispatcherServlet' to [/] 2014-03-05 10:57:51.702 INFO 45469 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
The following items are output:
ERROR
, WARN
, INFO
, DEBUG
or TRACE
.---
separator to distinguish the start of actual log messages.The default log configuration will echo messages to the console as they are written. By
default ERROR
, WARN
and INFO
level messages are logged. To also log DEBUG
level
messages to the console you can start your application with a --debug
flag.
$ java -jar myapp.jar --debug
Note | |
---|---|
you can also specify |
If your terminal supports ANSI, color output will be used to aid readability. You can set
spring.output.ansi.enabled
to a
supported value to override the auto
detection.
By default, Spring Boot will only log to the console and will not write log files. If you
want to write log files in addition to the console output you need to set a
logging.file
or logging.path
property (for example in your application.properties
).
The following table shows how the logging.*
properties can be used together:
Table 26.1. Logging properties
|
| Example | Description |
(none) | (none) | Console only logging. | |
Specific file | (none) |
| Writes to the specified log file. Names can be an exact location or relative to the current directory. |
(none) | Specific directory |
| Writes |
Log files will rotate when they reach 10 Mb and as with console output, ERROR
, WARN
and INFO
level messages are logged by default.
Note | |
---|---|
The logging system is initialized early in the application lifecycle and as such
logging properties will not be found in property files loaded via |
All the supported logging systems can have the logger levels set in the Spring
Environment
(so for example in application.properties
) using
‘logging.level.*=LEVEL’ where ‘LEVEL’ is one of TRACE, DEBUG, INFO, WARN, ERROR,
FATAL, OFF. Example application.properties
:
logging.level.org.springframework.web: DEBUG logging.level.org.hibernate: ERROR
Note | |
---|---|
By default Spring Boot remaps Thymeleaf |
The various logging systems can be activated by including the appropriate libraries on
the classpath, and further customized by providing a suitable configuration file in the
root of the classpath, or in a location specified by the Spring Environment
property
logging.config
. (Note however that since logging is initialized before the
ApplicationContext
is created, it isn’t possible to control logging from
@PropertySources
in Spring @Configuration
files. System properties and the
conventional Spring Boot external configuration files work just fine.)
Depending on your logging system, the following files will be loaded:
Logging System | Customization |
---|---|
Logback |
|
Log4j |
|
Log4j2 |
|
JDK (Java Util Logging) |
|
To help with the customization some other properties are transferred from the Spring
Environment
to System properties:
Spring Environment | System Property | Comments |
---|---|---|
|
| Used in default log configuration if defined. |
|
| Used in default log configuration if defined. |
|
| The current process ID (discovered if possible and when not already defined as an OS environment variable). |
All the logging systems supported can consult System properties when parsing their
configuration files. See the default configurations in spring-boot.jar
for examples.
Warning | |
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There are known classloading issues with Java Util Logging that cause problems when running from an ‘executable jar’. We recommend that you avoid it if at all possible. |