Java – Where/how does log4j look for a log4j.properties file

javalog4jlogging

I'm trying out log4j in a simple test app. I create a new Java project in eclipse and add the log4j JAR (v1.2.16) to my build path. I then create a simple class that prints Hello World. Then I use the log4j Logger class to log a info message. When I run the app, I see the log message, using what I assume is the default appender and layout. Great. What I'm having trouble with is adding my own configuration. This is what I've done:

Created a log4j.properties file with a custom appender and log level and placed it into the src folder (which upon compilation gets copied to the bin folder). Run the app – no change.

I try adding PropertyConfigurator.configure("log4j.properties"). Run the app – no change. No errors, but no change.

What do I have to do to get log4j to load my configuration file?

Best Answer

Look in the manual under the heading Default Initialization Procedure, where you'll find the following:

The exact default initialization algorithm is defined as follows:

Setting the log4j.defaultInitOverride system property to any other value than "false" will cause log4j to skip the default initialization procedure (this procedure).

Set the resource string variable to the value of the log4j.configuration system property. The preferred way to specify the default initialization file is through the log4j.configuration system property. In case the system property log4j.configuration is not defined, then set the string variable resource to its default value "log4j.properties".

Attempt to convert the resource variable to a URL.

If the resource variable cannot be converted to a URL, for example due to a MalformedURLException, then search for the resource from the classpath by calling org.apache.log4j.helpers.Loader.getResource(resource, Logger.class) which returns a URL. Note that the string "log4j.properties" constitutes a malformed URL. See Loader.getResource(java.lang.String) for the list of searched locations.

If no URL could not be found, abort default initialization. Otherwise, configure log4j from the URL. The PropertyConfigurator will be used to parse the URL to configure log4j unless the URL ends with the ".xml" extension, in which case the DOMConfigurator will be used. You can optionaly specify a custom configurator. The value of the log4j.configuratorClass system property is taken as the fully qualified class name of your custom configurator. The custom configurator you specify must implement the Configurator interface.

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Note that if you need to use i.remove(); in your loop, or access the actual iterator in some way, you cannot use the for ( : ) idiom, since the actual iterator is merely inferred.

As was noted by Denis Bueno, this code works for any object that implements the Iterable interface.

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If you put it somewhere in the classpath, Log4J will automatically load it. A typical place for it is the source (or resource) root directory. That way it can get copied into the root directory of your jar too (if you create one from your class files).

The exact details for this depend on what build system you use. E.g. in Maven the convention is to put it in src/main/resources.

Best Answer

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