how to set loglevel from INFO to ERROR using log4j

Question

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

Answer 1

On my side, i had to use this code in order to have this working fine (based on previous answers).

import org.apache.logging.log4j.core.LoggerContext;
import org.apache.logging.log4j.core.config.AbstractConfiguration;

...

public static void changeLoggerLevel(final String module, final Level level) {
  String moduleRenamed = module.replaceAll("/", ".");
  LoggerContext ctx = (LoggerContext)LogManager.getContext(false);
  AbstractConfiguration configuration = (AbstractConfiguration) ctx
        .getConfiguration();
  if (configuration.getLogger(moduleRenamed) != null) {
    LoggerConfig loggerConfig = configuration.getLoggerConfig(moduleRenamed);
    loggerConfig.setLevel(level);
  } else {
    LoggerConfig loggerConfig = new LoggerConfig(moduleRenamed, level, true);
    configuration.addLogger(moduleRenamed, loggerConfig);
  }
  ctx.updateLoggers(configuration);
}

The problem was with the getLoggerConfig() call; if the module you are trying to give a new level is not yet registered, this method returns the root logger (or any intermediate sub path registered), and thus instead of altering the level for com.mycompany you will alter root or com level. That's why you have to add a new LoggerConfig in case the module to alter is not yet registered.

Answer 2

Gary Gregory is correct.

Also the answer to this question is right there on the FAQ page in log4j2's site

https://logging.apache.org/log4j/2.x/faq.html#reconfig_level_from_code

Sample Code below:

Configurator.setLevel(logger.getName(), Level.INFO);

Answer 3

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 4

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.

Answer 5

The following APIs in the class org.apache.logging.log4j.core.config.Configurator allow you to change Levels:

• setAllLevels(String, Level)
• setLevel(Map)
• setLevel(String, Level)
• setRootLevel(Level)