How to log multiple threads in different log files?

Question

I have a JAVA class that starts various threads that have unique IDs. Each thread should log into a unique log file, named after the ID.log.

Because I only get the u

Answer 1

As far as I can tell ThreadLocal API was designed to do what you describe.

Code like below would establish per-thread loggers each using own (per-thread) FileAppender:

/**
 * usage: threadLocalLogger.get().info("hello thread local logger")
 */
static ThreadLocal threadLocalLogger = newThreadLocalLogger("myJobId");

private static ThreadLocal newThreadLocalLogger(final String myJobID) {
    return new ThreadLocal() {
        @Override
        protected Logger initialValue() {
            return logger(myJobID, Thread.currentThread().getId());
        }
    };
}

private static Logger logger(String myJobID, long threadId) {
    // Initialize the logger
    String loggerId = myJobID + "-" + threadId;
    Logger myLogger = Logger.getLogger(loggerId);
    FileAppender myFileAppender;
    try
    {
        myFileAppender = new FileAppender(new SimpleLayout(),
                loggerId + ".log", false);
        BasicConfigurator.resetConfiguration();
        BasicConfigurator.configure(myFileAppender);
    } catch (IOException e1) {
    // TODO Auto-generated catch block
        e1.printStackTrace();
    }
    return myLogger;
}