README.md

dynamic log level

A simple trick to change log level dynamically at runtime. You can copy all the code (only 2 files) into your project to use it. Please note the mechanism is designed for log4j 1.x, which is used widely in Java applications.

Usage

import org.apache.log4j.Logger;
import org.junit.Test;

public class Log4jLogLevelManagerTest {

  private static final Logger logger = Logger.getLogger("test");

  @Test
  public void test() {
    Log4jLogLevelManager manager = new Log4jLogLevelManager();

    // original level of logger 'test' is INFO
    logger.info("info message should be outputed");
    logger.debug("debug message should not be outputed");

    // change log level to debug
    manager.changeLogLevel("test", "DEBUG");

    logger.debug("debug message should be outputed now");

    // reset level of logger 'test'
    manager.resetLogLevel("test");

    logger.debug("debug message should not be outputed again");
  }

}

Log4jLogLevelManager

LogLevelManager is the main interface to manage the log level.

public interface LogLevelManager {

  void changeLogLevel(String loggerName, String level);

  void resetLogLevel(String loggerName);

}

Under the hood, Log4jLogLevelManager calls org.apache.log4j.LogManager to change log level.

In order to reset the log level, Log4jLogLevelManager pushes the original log level to an internal map and sets it back to logger when resetLogLevel is called. The map here is ConcurrentHashMap so you don't need to worry about the concurrent issues.

Feel free to use this trick if you want to change log level at runtime. It may help you a lot like inspecting an online problem but there's few logs, then you can change the log level to output more. :)