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

One possible solution is to create your own class which sits between your code and Log4J and appends the thread ID to every log message:

public class ThreadLogger
{
    // Constructor declared private to prevent instantiation.  Use static methods instead.
    private ThreadLogger() {}

    private static enum LogLevel
    {
        TRACE,
        DEBUG,
        INFO,
        WARN,
        ERROR
    }

    public static void trace(String message)
    {
        logMessage(message, LogLevel.ERROR);
    }

    public static void debug(String message)
    {
        logMessage(message, LogLevel.ERROR);
    }

    public static void info(String message)
    {
        logMessage(message, LogLevel.ERROR);
    }

    public static void warn(String message)
    {
        logMessage(message, LogLevel.WARN);
    }

    public static void error(String message)
    {
        logMessage(message, LogLevel.ERROR);
    }

    private static void logMessage(String message, LogLevel logLevel)
    {
        // Get the Log4J logger for the class that originally wanted to log the message
        String callingClassName = Thread.currentThread().getStackTrace()[3].getClassName();
        Class callingClass;
        try
        {
            callingClass = Class.forName(callingClassName);
        }
        catch(ClassNotFoundException e)
        {
            String errorMessage = String.format("Could not reference class [%s].  Unable to log call!", callingClassName);
            throw new RuntimeException(errorMessage);
        }
        Logger logger = Logger.getLogger(callingClass);

        // Get the thread ID and place it in front of the logged message
        long threadId = Thread.currentThread().getId();
        String formattedMessage = String.format("[%s] %s", threadId, message);

        // Log the message
        switch(logLevel)
        {
            case TRACE:
                logger.trace(formattedMessage);
                break;
            case DEBUG:
                logger.debug(formattedMessage);
                break;
            case INFO:
                logger.info(formattedMessage);
                break;
            case WARN:
                logger.warn(formattedMessage);
                break;
            case ERROR:
                logger.error(formattedMessage);
                break;
        }
    }
}

Downsides:

• Performance? This adds a few extra steps to every log statement.
• Stability? This adds a potential point of failure (the Class.forName call).
• You have to replace all of your existing log statements with calls to the new class.
• The thread ID won't appear until after the regular Log4J formatting. IE:

1234 [main] INFO com.foo.bar.Baz - [1] Hello world on thread #1!
1234 [main] INFO com.foo.bar.Baz - [2] Hello world on thread #2!