Apache Log4j Core Implementation provides the functional components of the logging system. Users are free to create their own plugins and include them in the logging configuration. Apache Log4j Core is a required module to use Apache Log4j.

Bytecode (Java 8) for Apache Log4j Core Implementation is provided in a separate JAR file like log4j-core-2.14.1.jar.

Source Code files for Apache Log4j API are provided in both binary packge like apache-log4j-2.14.1-bin.zip and source package like apache-log4j-2.14.1-src.zip. You can download them at Apache Log4j Website.

You can also browse Source Code files for Apache Log4j Core Implementation 2.14.1 below.

⏎ org/apache/logging/log4j/core/util/UuidUtil.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache license, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the license for the specific language governing permissions and
 * limitations under the license.
 */
package org.apache.logging.log4j.core.util;

import java.nio.ByteBuffer;
import java.security.SecureRandom;
import java.util.Random;
import java.util.UUID;
import java.util.concurrent.atomic.AtomicInteger;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.status.StatusLogger;
import org.apache.logging.log4j.util.PropertiesUtil;

/**
 * Generates a unique ID. The generated UUID will be unique for approximately 8,925 years so long as
 * less than 10,000 IDs are generated per millisecond on the same device (as identified by its MAC address).
 */
public final class UuidUtil {
    /**
     * System property that may be used to seed the UUID generation with an integer value.
     */
    public static final String UUID_SEQUENCE = "org.apache.logging.log4j.uuidSequence";

    private static final Logger LOGGER = StatusLogger.getLogger();

    private static final String ASSIGNED_SEQUENCES = "org.apache.logging.log4j.assignedSequences";

    private static final AtomicInteger COUNT = new AtomicInteger(0);
    private static final long TYPE1 = 0x1000L;
    private static final byte VARIANT = (byte) 0x80;
    private static final int SEQUENCE_MASK = 0x3FFF;
    private static final long NUM_100NS_INTERVALS_SINCE_UUID_EPOCH = 0x01b21dd213814000L;
    private static final long INITIAL_UUID_SEQNO = PropertiesUtil.getProperties().getLongProperty(UUID_SEQUENCE, 0);

    private static final long LOW_MASK = 0xffffffffL;
    private static final long MID_MASK = 0xffff00000000L;
    private static final long HIGH_MASK = 0xfff000000000000L;
    private static final int NODE_SIZE = 8;
    private static final int SHIFT_2 = 16;
    private static final int SHIFT_4 = 32;
    private static final int SHIFT_6 = 48;
    private static final int HUNDRED_NANOS_PER_MILLI = 10000;

    private static final long LEAST = initialize(NetUtils.getMacAddress());

    /* This class cannot be instantiated */
    private UuidUtil() {
    }

    /**
     * Initializes this class
     * 
     * @param mac MAC address
     * @return Least
     */
    static long initialize(byte[] mac) {
        final Random randomGenerator = new SecureRandom();
        if (mac == null || mac.length == 0) {
            mac = new byte[6];
            randomGenerator.nextBytes(mac);
        }
        final int length = mac.length >= 6 ? 6 : mac.length;
        final int index = mac.length >= 6 ? mac.length - 6 : 0;
        final byte[] node = new byte[NODE_SIZE];
        node[0] = VARIANT;
        node[1] = 0;
        for (int i = 2; i < NODE_SIZE; ++i) {
            node[i] = 0;
        }
        System.arraycopy(mac, index, node, 2, length);
        final ByteBuffer buf = ByteBuffer.wrap(node);
        long rand = INITIAL_UUID_SEQNO;
        String assigned = PropertiesUtil.getProperties().getStringProperty(ASSIGNED_SEQUENCES);
        long[] sequences;
        if (assigned == null) {
            sequences = new long[0];
        } else {
            final String[] array = assigned.split(Patterns.COMMA_SEPARATOR);
            sequences = new long[array.length];
            int i = 0;
            for (final String value : array) {
                sequences[i] = Long.parseLong(value);
                ++i;
            }
        }
        if (rand == 0) {
            rand = randomGenerator.nextLong();
        }
        rand &= SEQUENCE_MASK;
        boolean duplicate;
        do {
            duplicate = false;
            for (final long sequence : sequences) {
                if (sequence == rand) {
                    duplicate = true;
                    break;
                }
            }
            if (duplicate) {
                rand = (rand + 1) & SEQUENCE_MASK;
            }
        } while (duplicate);
        assigned = assigned == null ? Long.toString(rand) : assigned + ',' + Long.toString(rand);
        System.setProperty(ASSIGNED_SEQUENCES, assigned);

        return buf.getLong() | rand << SHIFT_6;
    }

    /**
     * Generates Type 1 UUID. The time contains the number of 100NS intervals that have occurred
     * since 00:00:00.00 UTC, 10 October 1582. Each UUID on a particular machine is unique to the 100NS interval
     * until they rollover around 3400 A.D.
     * <ol>
     * <li>Digits 1-12 are the lower 48 bits of the number of 100 ns increments since the start of the UUID
     * epoch.</li>
     * <li>Digit 13 is the version (with a value of 1).</li>
     * <li>Digits 14-16 are a sequence number that is incremented each time a UUID is generated.</li>
     * <li>Digit 17 is the variant (with a value of binary 10) and 10 bits of the sequence number</li>
     * <li>Digit 18 is final 16 bits of the sequence number.</li>
     * <li>Digits 19-32 represent the system the application is running on.</li>
     * </ol>
     *
     * @return universally unique identifiers (UUID)
     */
    public static UUID getTimeBasedUuid() {

        final long time = ((System.currentTimeMillis() * HUNDRED_NANOS_PER_MILLI) +
            NUM_100NS_INTERVALS_SINCE_UUID_EPOCH) + (COUNT.incrementAndGet() % HUNDRED_NANOS_PER_MILLI);
        final long timeLow = (time & LOW_MASK) << SHIFT_4;
        final long timeMid = (time & MID_MASK) >> SHIFT_2;
        final long timeHi = (time & HIGH_MASK) >> SHIFT_6;
        final long most = timeLow | timeMid | TYPE1 | timeHi;
        return new UUID(most, LEAST);
    }
}

⏎ org/apache/logging/log4j/core/util/UuidUtil.java

Or download all of them as a single archive file:

File name: log4j-core-2.14.1-sources.jar
File size: 1281358 bytes
Release date: 2021-03-06
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