Display thread id instead thread name in log

Question

I have a Struts application with log4j to display information about application.

The pattern to format log\'s output is as follows:

log4j.appender.RA         


        

Answer 1

Extend PatternLayout as below, and then specify MyPatternLayout with $X{threadId} in the format string.

This implementation uses ThreadLocal to minimize the performance impact of calculating the Thread ID:

    MyPatternLayout extends PatternLayout {

        private final ThreadLocal threadId = new ThreadLocal() {

            @Override
            protected String initialValue() {
                String t = Long.toString(Thread.currentThread().getId());
                MDC.put("threadId", t);
                return t;
            }
        };

        @Override
        public String format(LoggingEvent event) {

            this.threadId.get();
            return super.format(event);
        }
    }