Advantage of log4j

Question

What\'s the advantage of log4j over set System.out and System.err to output to a log file?

Answer 1

At a high level, the win from Log4j over manual logging is that you can decouple your logging code from what you actually want to log and where and how you want to log it. Details about logging verbosity/filtering, formatting, log location, and even log type (files, network, etc.) are handled declaratively using configuration and extensibly via custom appenders, rather you having to code that flexibility yourself.

This is critically important because it's often hard for developers to predict how logging needs will change once their software is in production. Operations teams managing that software may need less verbose logs, may need mulitple logs, may need to ship those logs to multiple servers, may need to sometimes get really verbose data for troubleshooting, etc. And it's usually impossible for operations teams, if they need to change how logging works, to convince the developer to make big code changes. This often leads to production downtime, friction between operations and development, and wasted time all around.

From the developer's point of view, Log4j insulates you from having to make code changes to support logging, and insulates you from being pestered by people who want logging changes. It enables people managing your code to scratch their own itch rather than bugging you!

Also, since Log4j is the de-facto standard for Java logging, there are lots of tools available which can do cool things with Log4j-- furthermore preventing you and your operations teams from re-inventing the wheel.

My favorite feature is the ability to easily write appenders send data to non-file sources, like SYSLOG, Splunk, etc. which makes it easy to your app's custom logging into operations management tools your IT department is already using.

Answer 2

log4j allows you to log to various resources e.g. event log, email, file system etc while allowing your application to remain decoupled from all of these resources. Furthermore, you get to use a common interface to log to all of the various resources without having to learn or integrate thier corresponding APIs.