how to set loglevel from INFO to ERROR using log4j2 api at runtime?

Question

logger.setLevel() method is not available in log4j2 API. So how to set log level at run time.

Answer 1

I'm not sure if this is the best way, but you set the level on org.apache.logging.log4j.core.config.LoggerConfig which you can get from the LoggerContext via the LogManager.

Once set, you can update the loggers with the new configuration.

As an example:

public static void main(String[] args) {
    Logger log = LogManager.getLogger(LogManager.ROOT_LOGGER_NAME);
    log.error("An error");
    log.debug("A debug");

    LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
    Configuration conf = ctx.getConfiguration();
    conf.getLoggerConfig(LogManager.ROOT_LOGGER_NAME).setLevel(Level.DEBUG);
    ctx.updateLoggers(conf);

    log.error("Another error");
    log.debug("Another debug");
}

Yields:

14:03:41.346 [main] ERROR  - An error
14:03:41.348 [main] ERROR  - Another error
14:03:41.348 [main] DEBUG  - Another debug

Answer 2

Credit to amcintosh, I wrapped their answer in a function:

/** Override the logging level of a given logger, return the previous level */
public static Level setLevel(Logger log, Level level) {
  LoggerContext ctx = (LoggerContext)LogManager.getContext(false);
  Configuration conf = ctx.getConfiguration();
  LoggerConfig lconf = conf.getLoggerConfig(log.getName());
  Level oldLevel = lconf.getLevel();
  lconf.setLevel(level);
  ctx.updateLoggers(conf);
  return oldLevel;
}

Despite amoe's comment, this seems to be working correctly for me using Log4J 2.5.