How To Re-read log4j.properties

I had a peculiar problem this morning. log4j logging output was being turned off in a call to a third party library¹. Not very much fun, particularly when exceptions start going unlogged.

Here are two code snippets that were useful for debugging the problem. This code resets the log4j configuration from the contents of the log4j.properties file:

static void resetLog4j() {
    LogManager.resetConfiguration();
    ClassLoader cl = this.getClass().getClassLoader();
    URL log4jprops = cl.getResource(
            "log4j.properties");
    if (log4jprops != null) {
        (new PropertyConfigurator())
                .configure(log4jprops);
    }
}

The log4j config can be dumped to standard out like this:

private void printLog4jConfig() {
    System.out.println("#log4j Config");
    PrintWriter pw = new PrintWriter(System.out);
    PropertyPrinter pp = new PropertyPrinter(pw);
    pp.print(pw);
    System.out.println("#End of Config");
}

¹ Google turned up a solution to the same problem in a previous version of the product, but nothing for the current version. I couldn’t find any other mention in the Knowledge Base or Support forums. I submitted a bug report, but meanwhile I have a workaround.