log4j configuration with Java Web Start

Question

Our Java WebStart application does not include a log4j configuration file; it simply sets up some hardcoded loggers and appenders.

I would like individual clients to be able to drop a log4j.properties file in somewhere and set up their own custom logging in troubleshooting situations. I could bundle a log4j.properties file into one of the jars of our application somewhere and that would allow configuration, but then the configuration would be the same for each client instead of only affecting the client that I want to troubleshoot. Plus, I wouldn't be able to change settings on the fly.

Is there a way I can hijack the log4j initialization procedure to use a per-client configuration file?

Answer 1

The basic problem here, is that Java Web Start severely restricts the access to the machine.

You should be able to do this, if you are running a signed application AND the user allows you full access to the machine. If not, you cannot do this with log4j with the default mechanism.

You may want to write your own configurator which reads from the file system using the Java WebStart API an then feeds that to log4j, but it will require some elbow grease.

Answer 2

You could use the PersistenceService to store the log4j configuration on the local user's machine (works without signing), or at least store a flag on whether to load a special config or not at startup of your web start application.

There is also a FileOpenService with which the end-user could open a local log4j.xml file to re-configure the logging facility on the fly. That way, the user has the control over the configuration and he has the control when and where to apply it.

Your app code which uses the FileOpenService to get the stream to the log4j configuration file can then use the DOMConfigurator.configure(InputStream) to reconfigure log4j.