How to Dynamically Change Spring Boot Log Levels Without Restart

Environment: Spring Boot 2.4.12.

When a project needs more detailed logs during runtime, developers often modify the configuration file and restart the service. This article shows how to change log levels dynamically without touching the configuration file or restarting.

Test Controller

package com.pack.logger.change_level;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/logger")
public class LoggerLevelChangeController {
    private static final Logger logger = LoggerFactory.getLogger(LoggerLevelChangeController.class);

    @GetMapping("/print")
    public Object print() {
        logger.info("This is Info logger...");
        logger.debug("This is Debug logger...");
        return "print";
    }
}

The default application.yml config sets the package log level to INFO:

logging:
  level:
    '[com.pack.logger.change_level]': INFO

Running the /logger/print endpoint prints only the INFO message because the logger is set to INFO.

Changing Log Level at Runtime

Add a method that uses LoggingSystem to set the level for the package:

@GetMapping("/level")
public Object changeLevel(String level) {
    LoggingSystem system = LoggingSystem.get(ClassLoader.getSystemClassLoader());
    // first argument: logger name, second: LogLevel parsed from request
    system.setLogLevel("com.pack.logger.change_level", resolveLogLevel(level));
    return "change logger level success";
}

private LogLevel resolveLogLevel(String level) {
    String trimmedLevel = level.trim();
    return LogLevel.valueOf(trimmedLevel.toUpperCase(Locale.ENGLISH));
}

Calling /logger/level?level=DEBUG changes the package logger to DEBUG. Subsequent calls to /logger/print now output both INFO and DEBUG messages without restarting the service.

Changing the Whole System Log Level

To adjust the root logger (affecting the entire application), modify the method to accept a logger name parameter. Passing root sets the name to null, which applies the level globally:

@GetMapping("/level")
public Object changeLevel(String name, String level) {
    LoggingSystem system = LoggingSystem.get(ClassLoader.getSystemClassLoader());
    if (name.equalsIgnoreCase("root")) {
        name = null;
    }
    system.setLogLevel(name, resolveLogLevel(level));
    return "change logger level success";
}

Calling /logger/level?name=root&level=DEBUG changes the root level to DEBUG, as shown in the following log output:

Disabling Logging

Extend the resolveLogLevel method to treat the value false as LogLevel.OFF:

private LogLevel resolveLogLevel(String level) {
    String trimmedLevel = level.trim();
    if ("false".equalsIgnoreCase(trimmedLevel)) {
        return LogLevel.OFF;
    }
    return LogLevel.valueOf(trimmedLevel.toUpperCase(Locale.ENGLISH));
}

Setting level=false disables logging for the specified logger.

With these endpoints, developers can dynamically control logging granularity in a running Spring Boot application without modifying configuration files or restarting the service.