Logging

I am new to Arduino and I know little. I want to have Logging, like log4j. I found one Arduino Playground - Logging, but are there some others libraries? Could some body provide the references?

You would do well to explain what log4j is, for those not familiar with it.

You would do well to explain what log4j does that you want to replicate.

You would do well to explain just where you expect the Arduino to create the log files that you want to look at later.

OK. Three good questions, but main is the last one.
Arduino connects to PC by USB (I never tried this, but everybody say that) and controls some processes by PINs and sketch. I would like to have in PC a log of Arduino work (times, actions, errors, warnings, etc…). It could be text or digital codes, like 0001, 0002…if Arduino is too restricted by memory or/and speed. If Arduino controls something, I want to know when and how he does it. Also I want to collect those logs for long time.
Apache Log4j is a Java-based logging utility

Apache Log4j is a Java-based logging utility

Not necessarily. We use log4j in the C# app I work on at work.

What it handles is tracking which class logs the event, when, etc., so all I have to do is say log.DebugFormat(what I want to log), and it handles all the rest.

The Arduino isn't going to do all of that, because support is not built into all the classes, and it has no file storage facility.

You can make the program on the PC as sophisticated as YOU want, time-stamping each entry it writes to the file, containing data it got from the serial port. All the Arduino is going to do is call Serial.print() to send data.