Logs and metrics in Java

As we all know we are more or less logs-dependent. The scope of this article is not to present a logging-framework within Java, but superior level of abstraction for collecting, storing and analyzing, also the way good logs can help us to have a better overview over what our software application does and how good it does that. But what are those logs and why we need them? I personally consider a log as a small point, but keep in mind that multiple points can draw a line and multiple lines a form or a direction that should be understood.