Subclassing org.apache.log4j.Logger without altering %C?

Question

To enable things like

logger.info("This is a formatted number: %.2f", number)

I decided to write a subclass of org.apache.log4j.Logger. I know, I could have written a wrapper class to achieve the same result but since I'm adding a lot of appenders to the logger at runtime I prefer to use inheritance.

The subclass looks like this:

public final class FormatLogger extends Logger {

private final static FormatLoggerFactory factory = new FormatLoggerFactory();

protected FormatLogger(String name) {
    super(name);
}

public static Logger getLogger(String name) {
    return Logger.getLogger(name, factory);
}

public void fatal(String formatter, Object... args)  {
    log(Level.FATAL, formatter, args);
}

public void log(Level level, String formatter, Object... args) {
    if (super.isEnabledFor(level)) {
        super.log(level, String.format(formatter, args));
    }
}
}

Everything works nicely - everything but one thing: the message text now adds the name of the logger subclass instead of the name of the class calling the logger. As pattern layout, I use the following format:

[%d{yyyyMMdd HHmmss}] %-5p [%t] %C: %m%n

i.e. things look like this:

[20110525 214515] INFO  [main] org.xyz.FormatLogger: This is a formatted number: 23.23

instead of:

[20110525 214515] INFO  [main] org.xyz.Main: This is a formatted number: 23.23

Is there some way to do such thing "properly" so that "%C" keeps printing the original class name?

Answer 1

I did something similar, but I ended up creating a wrapper and passing in the class name to it. Then with this class name I prepended it to the front of all the 4 logging levels which I was already wrapping anyway. It's quite messy, but I couldn't find another way of doing so. My logging statements now spit out the logger name then the package/class name. Its a bit cumbersome, but I'd rather have the extra information vs having not enough information.

Answer 2

The solution is quite simple: add a fully qualified class name (FQCN), i.e.:

static String FQCN = FormatLogger.class.getName() + ".";

The log(..) method must then be modified like this:

super.log(FQCN, level, String.format(formatter, args), null);

This is perfectly shown in the example MyLogger.java that comes with log4j. -1 for my own laziness!