Hi Mike,

in our app we implemented a REST-Service to reconfigure log4j2 at runtime.

It's mainly to apply changes to the configuration and call updateLoggers()

    LoggerContext loggerContext = (LoggerContext)
LogManager.getContext(false);
    Configuration configuration = loggerContext.getConfiguration();
    LoggerConfig loggerConfig = configuration.getLoggerConfig(loggerName);
    LoggerConfig specificConfig = loggerConfig;

    if (!loggerConfig.getName().equals(loggerName)) {
      specificConfig = new LoggerConfig(loggerName, level, true);
      specificConfig.setParent(loggerConfig);
      configuration.addLogger(loggerName, specificConfig);
    }
    specificConfig.setLevel(level);
    loggerContext.updateLoggers();

see attachment for our full Log4j2Util code.

Regards,
  Volker



2018-02-08 21:28 GMT+01:00 Mike Kienenberger <mkien...@gmail.com>:

> As others have reported in years past, the examples in the docs for
>
> Programmatically Modifying the Current Configuration after Initialization
>
> are out of date.  They don't compile.  They don't work (affect the
> existing logging) even if you do fix the errors.
>
> Here's my situation:
>
> I am working in an environment with EVIL.JAR which includes a log4j2.xml
> file.
> I can't change the jar.  I can't specific a System Property to override it.
>
> My code gets called as a loaded module long after the logging system
> is initialized.
>
> I want logging in my own code to go to a different location, and
> preferably I'd like to read the configuration in from a log4j2.xml
> file so that anyone who uses my module isn't victim to the same evil
> hardcoded-logging practices of EVIL.JAR.
>
> Creating an XMLConfiguration and initializing it lets me read the xml
> file easily enough.   Looping through the data gets me the Appenders,
> Filters and Loggers.   But I still can't use them to modify the
> existing configuration.
>
> Another person took the approach of using JUL instead.  I hate JUL and
> I'd really rather not have to go down that route.
>
> Thanks in advance.
> -Mike
>
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-- 
inexso - information exchange solutions GmbH
Ofener Stra├če 30 | 26121 Oldenburg
www.inexso.de
package de.inexso.commons.logging;

import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.core.LoggerContext;
import org.apache.logging.log4j.core.appender.AbstractAppender;
import org.apache.logging.log4j.core.appender.ConsoleAppender;
import org.apache.logging.log4j.core.appender.FileAppender;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.LoggerConfig;
import org.apache.logging.log4j.core.layout.PatternLayout;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Log4j2Util {

  private static final Logger LOG = LoggerFactory.getLogger(Log4j2Util.class);

  public static void setLoggerLevel(String loggerName, String levelName) throws IllegalArgumentException {
    Level level = toLevel(levelName);
    setLoggerLevel(loggerName, level);
  }

  public static Level toLevel(String levelName) throws IllegalArgumentException {
    Level level = Level.toLevel(levelName, null);
    if (level == null) {
      throw new IllegalArgumentException("Unknown levelName \"" + levelName + "\"");
    }
    return level;
  }

  public static void setLoggerLevel(Configuration configuration, String loggerName, String levelName)
      throws IllegalArgumentException {
    setLoggerLevel(configuration, loggerName, toLevel(levelName));
  }

  public static void setLoggerLevel(String loggerName, Level level) {
    LoggerContext loggerContext = (LoggerContext) LogManager.getContext(false);
    Configuration configuration = loggerContext.getConfiguration();
    setLoggerLevel(configuration, loggerName, level);
    loggerContext.updateLoggers();
  }

  public static void setLoggerLevel(Configuration configuration, String loggerName, Level level) {
    LoggerConfig loggerConfig = configuration.getLoggerConfig(loggerName);
    LoggerConfig specificConfig = loggerConfig;

    if (!loggerConfig.getName().equals(loggerName)) {
      specificConfig = new LoggerConfig(loggerName, level, true);
      specificConfig.setParent(loggerConfig);
      configuration.addLogger(loggerName, specificConfig);
    }
    specificConfig.setLevel(level);
  }

  public static void replaceRootAppender(Configuration configuration, String appenderName, String logFileName, String logLayout) {
    AbstractAppender logAppender;
    if ("STDOUT".equalsIgnoreCase(logFileName)) {
      logAppender = ConsoleAppender.newBuilder()
          .withLayout(PatternLayout.newBuilder().withPattern(logLayout).build())
          .withName(appenderName)
          .build();
    } else {
      logAppender = FileAppender.newBuilder()
          .withFileName(logFileName)
          .withAppend(true)
          .withLayout(PatternLayout.newBuilder().withPattern(logLayout).build())
          .withName(appenderName)
          .build();
    }
    logAppender.start();

    LoggerConfig rootLogger = configuration.getRootLogger();
    rootLogger.removeAppender(appenderName);
    rootLogger.addAppender(logAppender, null, null);
  }

  public static void createFileAppender(String name, String fileName, String pattern) {
    LoggerContext loggerContext = (LoggerContext) LogManager.getContext(false);
    Configuration configuration = loggerContext.getConfiguration();

    FileAppender fileAppender = FileAppender.newBuilder()
        .withFileName(fileName)
        .withAppend(true)
        .withLayout(PatternLayout.newBuilder().withPattern(pattern).build())
        .withName(name)
        .build();
    configuration.addAppender(fileAppender);

    loggerContext.updateLoggers();
  }

  public static void createLogger(String name, String level, boolean additive, String appenderName) {
    LoggerContext loggerContext = (LoggerContext) LogManager.getContext(false);

    if (loggerContext.hasLogger(name)) {
      LOG.warn("logger \"{}\" already exists!", name);
    }
    Configuration configuration = loggerContext.getConfiguration();

    LoggerConfig loggerConfig = new LoggerConfig(name, toLevel(level), true);
    loggerConfig.setAdditive(additive);
    loggerConfig.addAppender(configuration.getAppender(appenderName), null, null);
    configuration.addLogger(name, loggerConfig);

    loggerContext.updateLoggers();
  }

}
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