How to Dynamically Change Log Levels in Spring Boot 1.5 Using the /loggers Endpoint

Overview

Spring Boot 1.5.x introduced a new actuator endpoint /loggers that allows developers to change the logging level of a running application on the fly. The endpoint is automatically enabled when the spring-boot-starter-actuator dependency is present.

Project Setup

Start with a basic Spring Boot project (for example, generated via Spring Initializr) and add the following dependencies to pom.xml:

<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>1.5.1.RELEASE</version>
  <relativePath/>
</parent>

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
</dependencies>

Include a simple REST controller that logs messages at different levels:

@RestController
@SpringBootApplication
public class DemoApplication {

    private Logger logger = LoggerFactory.getLogger(getClass());

    @RequestMapping(value = "/test", method = RequestMethod.GET)
    public String testLogLevel() {
        logger.debug("Logger Level ：DEBUG");
        logger.info("Logger Level ：INFO");
        logger.error("Logger Level ：ERROR");
        return "";
    }

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

To avoid the default security check that blocks the actuator endpoints, add the following line to application.properties:

management.security.enabled=false

Testing the Application

Run the application and call /test. The console will show INFO and ERROR messages (DEBUG is not printed because the default level is INFO):

2017-01-31 22:34:57.123  INFO 16372 --- [nio-8000-exec-1] ... : Logger Level ：INFO
2017-01-31 22:34:57.124  ERROR 16372 --- [nio-8000-exec-1] ... : Logger Level ：ERROR

Changing Log Level via POST

Send a POST request to /loggers/com.didispace with the JSON body {"configuredLevel": "DEBUG"}. The response confirms the change:

{
  "configuredLevel": "DEBUG"
}

After the change, call /test again. The console now includes the DEBUG line:

2017-01-31 22:37:35.252 DEBUG 16372 --- [nio-8000-exec-5] ... : Logger Level ：DEBUG
2017-01-31 22:37:35.252  INFO 16372 --- [nio-8000-exec-5] ... : Logger Level ：INFO
2017-01-31 22:37:35.252 ERROR 16372 --- [nio-8000-exec-5] ... : Logger Level ：ERROR

Viewing Current Log Level via GET

A GET request to /loggers/com.didispace returns the current configuration:

{
  "configuredLevel": "DEBUG",
  "effectiveLevel": "DEBUG"
}

Calling /loggers without a specific package lists all logger configurations (output omitted for brevity).

Key Takeaways

The /loggers actuator endpoint provides a lightweight way to adjust logging levels at runtime, which is useful for troubleshooting production issues without restarting the application.