Is there a proper way to timestamp console output using the default Java libraries?

Question

When I work on personal Java projects, I like to have a way of nicely logging text to console. I generally make some public static class for this to handle prefixing and applying a timestamp to the message so I can omit the usage of System.out.println(“Text”); .

This is a class I wrote a while ago and I tend to reuse it on different projects because I really like the way it formats the text:

import java.text.SimpleDateFormat;
import java.util.Date;

public class Log {

    public static final int LEVEL_INFO = 0;
    public static final int LEVEL_WARNING = 1;
    public static final int LEVEL_ERROR = 2;

    private static SimpleDateFormat df = new SimpleDateFormat("HH:mm:ss");
    /**
     * Used instead of System.out.println for consistent formatting.
     *
     * @param messageToPrefix Message that you want to send to print.
     * @param errorLevel Type of message you want to send.
     */
    public static void print(String messageToPrefix, int errorLevel) {
        StringBuilder message = new StringBuilder();
        message.append("[").append(df.format(new Date())).append("] ");
        switch(errorLevel) {
            case LEVEL_INFO:
                 message.append("[Info] ");
                break;
            case LEVEL_WARNING:
                message.append("[Warning] ");
                break;
            case LEVEL_ERROR:
                message.append("[Error] ");
                break;
        }
        message.append(messageToPrefix);
        System.out.println(message.toString());
    }
}

This is all works as expected but there is a small problem I noticed a while ago: this way of creating a timestamp is very resource intensive! Calling this requires the code I want to log to halt until the timestamp has been made and written to console. This just seems inefficient to me (even tho we are talking about several milliseconds here). I came to this conclusion when I compared the runtime of this logging method to one that used System.currentTimeMillis() which does not format it to a nice timestamp but shows the runtime in ms if used like this:

public class Log {

    private static final long startTime = System.currentTimeMillis();

    public static final int LOG_LEVEL_INFO = 0;
    public static final int LOG_LEVEL_WARNING = 1;
    public static final int LOG_LEVEL_ERROR = 2;
    public static final int LOG_LEVEL_UNKNOWN = 3;

    /**
     * Used instead of System.out.println for consistent formatting.
     *
     * @param msg Message that you want to send to log.
     * @param importance How important is the message?
     */
    public static void print(String msg, int importance) {
        StringBuilder finalMsg = new StringBuilder();
        finalMsg.append("[").append(System.currentTimeMillis() - startTime).append(" ms] ");
        switch (importance) {
            case 0:
                finalMsg.append("[INFO] ");
                break;
            case 1:
                finalMsg.append("[WARNING] ");
                break;
            case 2:
                finalMsg.append("[ERROR] ");
                break;
            default:
                finalMsg.append("[UNKNOWN] ");
                break;
        }
        finalMsg.append(msg);
        System.out.println(finalMsg);
    }
}

This way proved to be way faster even on a small scale like 50 messages over approx. 50 seconds of running time.

This got me thinking about several questions: Is there a better way for creating timestamps like this? Is there a way to not wait for the logging code to complete? Would starting a thread for this be a good idea? Or am I on a completely wrong track altogether?

I would like to not use any extra libraries for this to keep it small and simple.

Any advice would be much appreciated!

Answer 1

EDIT: Alright I think that (after following some advise) that this is a safe way to log and timestamp messages. It may not be the fastest method but it is safe to use and gives me the result I want.

import java.text.SimpleDateFormat;
import java.util.Date;

    public class Log {

        public static final int LEVEL_INFO = 0;
        public static final int LEVEL_WARNING = 1;
        public static final int LEVEL_ERROR = 2;

        private static final ThreadLocal<SimpleDateFormat> formatter = ThreadLocal.withInitial(() -> new SimpleDateFormat("HH:mm:ss"));

        /**
         * Used instead of System.out.println for consistent formatting.
         *
         * @param messageToPrefix Message that you want to send to print.
         * @param errorLevel Type of message you want to send.
         */
        public static void print(String messageToPrefix, int errorLevel) {
            StringBuilder message = new StringBuilder();
            message.append("[").append(formatter.get().format(new Date())).append("] ");
            switch(errorLevel) {
                case LEVEL_INFO:
                    message.append("[Info] ");
                    break;
                case LEVEL_WARNING:
                    message.append("[Warning] ");
                    break;
                case LEVEL_ERROR:
                    message.append("[Error] ");
                    break;
            }
            message.append(messageToPrefix);
            System.out.println(message.toString());
        }
    }

I want to thank the people in the comments for all the advice they gave.