Question

I’m confused as to how the errors are logged without me implicitly catching them and logging out the error. All that I’ve done is put a log4j.xml file in my project defining appenders and now the logs catch and log everything from the frameworks.
If I say, try to query in Hibernate and the query fails, or I try to open a file that doesn’t exist, or I get a null pointer exception, if the log4j.xml file defines a log file, and the error level is set correctly, then the error will be captured there?

How does my spring web app capture errors that I didn’t catch and log? Is this a result of apache commons logging?

Or is this some magic that log4j knows how to deal with – catch stream to the console etc?
Any info appreciated.

Answer 1

From spring official documentation:

The nice thing about commons-logging is that you don’t need anything else to make your application work. It has a runtime discovery algorithm that looks for other logging frameworks in well known places on the classpath and uses one that it thinks is appropriate (or you can tell it which one if you need to). If nothing else is available you get pretty nice looking logs just from the JDK (java.util.logging or JUL for short). You should find that your Spring application works and logs happily to the console out of the box in most situations, and that’s important.

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To make Log4j work with the default JCL dependency (commons-logging)
all you need to do is put Log4j on the classpath, and provide it with
a configuration file (log4j.properties or log4j.xml in the root of the
classpath).

Take a look for a complete explanation: http://static.springsource.org/spring/docs/3.0.x/reference/overview.html#d0e743