What is Log4j?

Log4j:

Log4j is a framework written in java which is highly configurable.

Here one question may come that what do we mean by “Framework” ?

Framework is nothing but a partially or semi build application. One can use it for building other software.

Log4j is used in java application for writing log in the code. Jar file (or dependency if you use Maven) need to be added to the project if you want to use log4j.