How to get distinct loggers in log4j?

Question

If my log4j.properties looks this

# General configuration
log4j.rootLogger = ERROR, ConsoleAppender

# Appender configuration
log4j.appender.ConsoleAppender = org.apache.log4j.ConsoleAppender
log4j.appender.ConsoleAppender.layout = org.apache.log4j.PatternLayout 
log4j.appender.ConsoleAppender.layout.ConversionPattern = %5p (%c) %m%n
#Other Loggers
log4j.logger.com.foo=INFO
log4j.logger.com.foo.Bar=DEBUG
log4j.logger.org.springframework=INFO

Is there an easy way to get just the loggers com.foo, com.foo.Bar, root, and org.springframework. And not the specific classes that have been created and inherit the levels (I.E. com.foo.bar.Baz?
For my purposes I want to create an admin page that displays these loggers and their levels, but not ALL loggers, just the ones that have been directly configured via properties. currently, I am traversing up the parent hierarchy until I come across a logger that has a different level that its parent, but that can hide some configured loggers if they are in the hierarchy and set the same level as something higher up.

Answer 1

You could do something like this. First get all loggers from the log manager:

Enumeration<Category> loggers = LogManager.getCurrentLoggers();

Then you can ask each logger for its level:

Level currentLevel = logger.getLevel();

currentLevel will be null if it has never been explicitly set. So, if the logger was set to a specific level in log4j.properties, you will get a non-null value. Else you will get a null value. The root logger always reports a level, so that would be a special case. This way, you would not need to parse the log4j.properties file.

The only problem is that if somewhere in your code you invoke setLevel() on a logger, it will also report non-null and appear on your list. That is because log4j does not know how a level was set, only if it was set at all. To distinguish these two cases, you would still need to parse log4j.properties.

Also, keep in mind that this works only on loggers which are currently loaded. So if com.foo.Bar was never loaded, you will not see it on your list even if it is explicitly mentioned in log4j.properties. Log4J does not know about non-existing loggers which might be created in the future. Again, for this you would need to parse log4j.properties.