GarbageFreeClock.java

package com.vizor.unreal.util.util;

import java.time.ZonedDateTime;

public class GarbageFreeClock
{
    private static final int msInSec = 1000;
    private static final int msInMin = msInSec * 60;
    private static final int msInHou = msInMin * 60;
    private static final int msInDay = msInHou * 24;

    private static final int patternLength = "HH:MM:SS:ZZZ".length();
    private static final int msZoneOffset = ZonedDateTime.now().getOffset().getTotalSeconds() * msInSec;

    private static final long bulkBufferSize = 100;
    private static final char[] bulkBuffer = new char[(int)(patternLength * bulkBufferSize)];

    private static String concatenate(long threadId, int h, int m, int s, int z)
    {
        final char buf[];
        final int initOffset;

        // fail-safe, but true sharing is possible
        if (threadId < bulkBufferSize)
        {
            buf = bulkBuffer;
            initOffset = (int)threadId;
        }
        else
        {
            buf = new char[patternLength];
            initOffset = 0;
        }

        int offset = initOffset;

        // hour
        buf[offset++] = (char)('0' + h / 10);
        buf[offset++] = (char)('0' + h % 10);
        buf[offset++] = ':';

        // min
        buf[offset++] = (char)('0' + m / 10);
        buf[offset++] = (char)('0' + m % 10);
        buf[offset++] = ':';

        // sec
        buf[offset++] = (char)('0' + s / 10);
        buf[offset++] = (char)('0' + s % 10);
        buf[offset++] = ':';

        // ms
        buf[offset++] = (char)('0' + z / 100);
        buf[offset++] = (char)('0' + ((z / 10) % 10));
        buf[offset  ] = (char)('0' + z % 10);

        return new String(buf, initOffset, patternLength);
    }

    private static String computeTime(final int rawMilliseconds)
    {
        int z = rawMilliseconds;

        // Disintegrate into parts
        final int h = z / msInHou;
        z -= (h * msInHou);

        final int m = z / msInMin;
        z -= (m * msInMin);

        final int s = z / msInSec;
        z -= (s * msInSec);

        return concatenate(Thread.currentThread().getId(), h, m, s, z);
    }

    public static String currentUtcTime()
    {
        final long currentTimeMillis = System.currentTimeMillis();
        return computeTime((int)(currentTimeMillis % msInDay));
    }

    public static String currentLocalTime()
    {
        final long currentTimeMillis = System.currentTimeMillis();
        return computeTime((int)((currentTimeMillis + msZoneOffset) % msInDay));
    }
}