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 unique ID at runtime, I have to configure Log4J programatically:

// Get the jobID
myJobID = aJobID;
// Initialize the logger
myLogger = Logger.getLogger(myJobID);
FileAppender myFileAppender;
try
{
    myFileAppender = new FileAppender(new SimpleLayout(), myJobID + ".log", false);
    BasicConfigurator.resetConfiguration();
    BasicConfigurator.configure(myFileAppender);
} catch (IOException e1) {
// TODO Auto-generated catch block
    e1.printStackTrace();
}

Now this works fine if I start jobs sequentially - but when I start 2 threads (of the same class) simultaneously, both logs are created but the logs are mixed up: The second thread logs into the first as well as the second log.

How could I make sure that each instance is unique ? I already tried to give a unique name to each logger instance, but it did not change anything.

Answer 1

Logback has a special appender called SiftingAppender which provides a very nice solution to the type of problems you describe. A SiftingAppender can be used to separate (or sift) logging according to any runtime attribute, including thread id.