Log4j: How to configure simplest possible file logging?

Question

My story:

I want to make a thing which is as simple as a simplest possible log4j logger that logs rows to a file. I have found several examples with some fun

Answer 1

Log4j can be a bit confusing. So lets try to understand what is going on in this file: In log4j you have two basic constructs appenders and loggers.

Appenders define how and where things are appended. Will it be logged to a file, to the console, to a database, etc.? In this case you are specifying that log statements directed to fileAppender will be put in the file sample.log using the pattern specified in the layout tags. You could just as easily create a appender for the console or the database. Where the console appender would specify things like the layout on the screen and the database appender would have connection details and table names.

Loggers respond to logging events as they bubble up. If an event catches the interest of a specific logger it will invoke its attached appenders. In the example below you have only one logger the root logger - which responds to all logging events by default. In addition to the root logger you can specify more specific loggers that respond to events from specific packages. These loggers can have their own appenders specified using the appender-ref tags or will otherwise inherit the appenders from the root logger. Using more specific loggers allows you to fine tune the logging level on specific packages or to direct certain packages to other appenders.

So what this file is saying is:

1. Create a fileAppender that logs to file sample.log
2. Attach that appender to the root logger.
3. The root logger will respond to any events at least as detailed as 'debug' level
4. The appender is configured to only log events that are at least as detailed as 'info'

The net out is that if you have a logger.debug("blah blah") in your code it will get ignored. A logger.info("Blah blah"); will output to sample.log.

The snippet below could be added to the file above with the log4j tags. This logger would inherit the appenders from but would limit the all logging events from the package org.springframework to those logged at level info or above.