How to configure Logger Programmatically in log4j2.02?

Question

I want to use log4j without any configure file. What I wan to do is something as:

logger = (Logger) LogManager.getLogger(this.getClass());
String pattern = "[%level] %m%n";
//do something to make this logger output to an local file "/xxx/yyy/zzz.log"

I have found this answer: Configuring Log4j Loggers Programmatically.

But the docs of Logger#addAppender says: This method is not exposed through the public API and is used primarily for unit testing.

I am not sure if it is the right way to use this method in my code or there is other better solution to solve my problem.

Answer 1

The official documentation shows an example : Programatically Adding to the Current Configuration

final LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
final Configuration config = ctx.getConfiguration();

Layout layout = PatternLayout.createLayout(PatternLayout.SIMPLE_CONVERSION_PATTERN, config, null, null,null, null);
Appender appender = FileAppender.createAppender("target/test.log", "false", "false", "File", "true", "false", "false", "4000", layout, null, "false", null, config);
appender.start();
config.addAppender(appender);

AppenderRef ref = AppenderRef.createAppenderRef("File", null, null);
AppenderRef[] refs = new AppenderRef[] {ref};
LoggerConfig loggerConfig = LoggerConfig.createLogger("false", "info", "org.apache.logging.log4j", "true", refs, null, config, null );
loggerConfig.addAppender(appender, null, null);
config.addLogger("org.apache.logging.log4j", loggerConfig);
ctx.updateLoggers();

With these limitations :

1. If the configuration file is changed the configuration will be reloaded and the manual changes will be lost.
2. Modification to the running configuration requires that all the methods being called (addAppender and addLogger) be synchronized.

This solution avoids to use method from the core implementation org.apache.logging.log4j.core.Logger, and it avoids dirty cast like that :

import org.apache.logging.log4j.Logger;

Logger logger = (Logger) LogManager.getLogger(this.getClass());
((org.apache.logging.log4j.core.Logger) logger).addAppender(...); // Bypassing the public API 

Answer 2

With the latest version of log4j2, all create the APIs like

PatternLayout.createLayout, 
FileAppender.createAppender, 
LoggerConfig.createLogger 

have become deprecated, it's better to use a custom log ConfigurationFactory along with ConfigurationBuilder for defining the log configuration programmatically.