Logging in web applications: Best practices?

Question

During deployment of a web application (in test environment) on customer site we encountered a problem with logging of the application. I'll shortly try to describe the current situation:

• Implementation uses Logger retrieved by java.util.logging and apache.commons.logging.
• In the deployed packages exists a commons-logging.properties pointing to JUL.
• Application is running on Tomcat 6.x

The customer decided that he wants to use Log4J on tomcat and configured it so it works (generally) - of course it's not working for the mentioned application.

As it seems that we need to change logging implementation anyway - i wanted to ask you for some best practices on how to implement logging in a web application. Following things should be possible:

• Customer needs to be able to change log-level without modifying anything in the *.war-file. -> If he would have to modify the war-file he would have to do this for every new build ...
• It should be possible to have some kind of rolling-file-logging (eg: max 10 files with max. 10mb each) - of course it should also be up to the customer to define and change this setting ...
• As another customer might want to use standard JUL-logging instead - I'd of course prefer to not hard-code the preferred library (Log4J in this case).

Answer 1

Customer needs to be able to change log-level without modifying anything in the *.war-file.

You can put logging framework configuration file ( log4j.xml or logback.xml ) outside of the WAR file. Also logback supports automatic reconfiguration when this file is changed.

It should be possible to have some kind of rolling-file-logging

Both log4j and Logback support rolling back of files, both based on size and date, see eg RollingFileAppender .

As another customer might want to use standard JUL-logging instead - I'd of course prefer to not hard-code the preferred library (Log4J in this case).

apache-commons-logging is fundamentally broken , use slf4j instead. Then you simply put different implementations on your CLASSPTH. Also the SLF4J API is quite pleasent.

Answer 2

You should take a look at SLF4J . It is essentially a wrapper that allows the end user to drop in what ever logging library they want (for the most part).

While I have not tried, they even have a migrator tool that should help changing over your code to use it.