Spring Boot Logging

Below is shown the code for a simple and fast way for log messages in a Spring Boot web application.

Dependencies

You don’t need any additional dependencies, Spring Boot already have all what is need. Only make sure you have at least the version 1.2.0 of Spring Boot.

Log object

Add the org.slf4j.Logger object on each java class where you want to log something:

package netgloo;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

// ...

public class SomeClass {

  // Define the logger object for this class
  private final Logger log = LoggerFactory.getLogger(this.getClass());

  // The rest of the class
  // ...

}

Inside class’s methods you can now use the log object for write messages at some log level:

  public void someMethod() {
    // ...    

    // Log a simple message
    log.debug("debug level log");
    log.info("info level log");
    log.error("error level log");

    // ...
  }

You will see your log messages in the Spring Boot’s console output, like this:

2016-05-22 12:00:06.589 DEBUG 9872 --- [nio-8080-exec-1] netgloo.controllers.HomeController    : debug level log
2016-05-22 12:00:06.590  INFO 9872 --- [nio-8080-exec-1] netgloo.controllers.HomeController    : info level log
2016-05-22 12:00:06.593 ERROR 9872 --- [nio-8080-exec-1] netgloo.controllers.HomeController    : error level log

You can also put your log in a file setting the logging.file configuration in the application.properties file (see below the Further configurations section).

Application.properties

Finally, in the application.properties file you can define the log level for your loggers:

src/main/resources/application.properties

# Level for loggers on classes inside the root package "netgloo" (and its 
# sub-packages)
# Available levels are: TRACE, DEBUG, INFO, WARN, ERROR, FATAL, OFF
logging.level.netgloo = DEBUG

If you define the INFO level for the package netgloo then all logs printed using the info method up to the fatal will be printed out, while debug ones will be ignored.

That’s all.

Further configurations

Logging formatted string
It is possible to log formatted string using the following format:

log.info("another info log with {}, {} and {} arguments", 1, "2", 3.0);

Additional configurations in the application.properties
In the application.properties file you can put some additional configurations:

# Fine-tuning a specific logger (for a single class)
logging.level.netgloo.controllers.HomeController = TRACE

# Specify the level for spring boot and hibernate's loggers
logging.level.org.springframework.web = DEBUG
logging.level.org.hibernate = ERROR

# Log file location (in addition to the console)
logging.file = /var/netgloo_blog/logs/application.log

Logback
As said in the official reference, Spring Boot use Logback by default as logging service. You can set advanced configurations using the logback.xml file, placing it in src/main/resources/logback.xml (so Maven or Gradle will copy it in the classpath root). See here and here for two simple examples about the logback configuration file.

Try the code yourself

Try yourself getting the code for this post from our github repository:

https://github.com/netgloo/spring-boot-samples/tree/master/spring-boot-logging

References

http://docs.spring.io/spring-boot/docs/1.2.0.RELEASE/reference/html/howto-logging.html
https://wiki.base22.com/display/btg/How+to+setup+SLF4J+and+LOGBack+in+a+web+app+-+fast
http://www.javacodegeeks.com/2011/12/configure-logback-logging-with-spring.html
https://stackoverflow.com/questions/8262310/any-reason-to-use-private-instead-of-private-final-static-on-the-logback-logger