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/impl/ReusableLogEventFactory.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.impl;

import java.util.List;

import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.Marker;
import org.apache.logging.log4j.ThreadContext;
import org.apache.logging.log4j.core.ContextDataInjector;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.async.ThreadNameCachingStrategy;
import org.apache.logging.log4j.core.config.Property;
import org.apache.logging.log4j.core.util.Clock;
import org.apache.logging.log4j.core.util.ClockFactory;
import org.apache.logging.log4j.message.Message;
import org.apache.logging.log4j.util.StringMap;

/**
 * Garbage-free LogEventFactory that reuses a single mutable log event.
 * @since 2.6
 */
public class ReusableLogEventFactory implements LogEventFactory, LocationAwareLogEventFactory {
    private static final ThreadNameCachingStrategy THREAD_NAME_CACHING_STRATEGY = ThreadNameCachingStrategy.create();
    private static final Clock CLOCK = ClockFactory.getClock();

    private static ThreadLocal<MutableLogEvent> mutableLogEventThreadLocal = new ThreadLocal<>();
    private final ContextDataInjector injector = ContextDataInjectorFactory.createInjector();

    /**
     * Creates a log event.
     *
     * @param loggerName The name of the Logger.
     * @param marker An optional Marker.
     * @param fqcn The fully qualified class name of the caller.
     * @param level The event Level.
     * @param message The Message.
     * @param properties Properties to be added to the log event.
     * @param t An optional Throwable.
     * @return The LogEvent.
     */
    @Override
    public LogEvent createEvent(final String loggerName, final Marker marker,
        final String fqcn, final Level level, final Message message,
        final List<Property> properties, final Throwable t) {
        return createEvent(loggerName, marker, fqcn, null, level, message, properties, t);
    }

    /**
     * Creates a log event.
     *
     * @param loggerName The name of the Logger.
     * @param marker An optional Marker.
     * @param fqcn The fully qualified class name of the caller.
     * @param location The location of the caller.
     * @param level The event Level.
     * @param message The Message.
     * @param properties Properties to be added to the log event.
     * @param t An optional Throwable.
     * @return The LogEvent.
     */
    @Override
    public LogEvent createEvent(final String loggerName, final Marker marker, final String fqcn,
                                final StackTraceElement location, final Level level, final Message message,
                                final List<Property> properties, final Throwable t) {
        MutableLogEvent result = mutableLogEventThreadLocal.get();
        if (result == null || result.reserved) {
            final boolean initThreadLocal = result == null;
            result = new MutableLogEvent();

            // usually no need to re-initialize thread-specific fields since the event is stored in a ThreadLocal
            result.setThreadId(Thread.currentThread().getId());
            result.setThreadName(Thread.currentThread().getName()); // Thread.getName() allocates Objects on each call
            result.setThreadPriority(Thread.currentThread().getPriority());
            if (initThreadLocal) {
                mutableLogEventThreadLocal.set(result);
            }
        }
        result.reserved = true;
        result.clear(); // ensure any previously cached values (thrownProxy, source, etc.) are cleared

        result.setLoggerName(loggerName);
        result.setMarker(marker);
        result.setLoggerFqcn(fqcn);
        result.setLevel(level == null ? Level.OFF : level);
        result.setMessage(message);
        result.initTime(CLOCK, Log4jLogEvent.getNanoClock());
        result.setThrown(t);
        result.setSource(location);
        result.setContextData(injector.injectContextData(properties, (StringMap) result.getContextData()));
        result.setContextStack(ThreadContext.getDepth() == 0 ? ThreadContext.EMPTY_STACK : ThreadContext.cloneStack());// mutable copy

        if (THREAD_NAME_CACHING_STRATEGY == ThreadNameCachingStrategy.UNCACHED) {
            result.setThreadName(Thread.currentThread().getName()); // Thread.getName() allocates Objects on each call
            result.setThreadPriority(Thread.currentThread().getPriority());
        }
        return result;
    }

    /**
     * Switches the {@code reserved} flag off if the specified event is a MutableLogEvent, otherwise does nothing.
     * This flag is used internally to verify that a reusable log event is no longer in use and can be reused.
     * @param logEvent the log event to make available again
     * @since 2.7
     */
    public static void release(final LogEvent logEvent) { // LOG4J2-1583
        if (logEvent instanceof MutableLogEvent) {
            final MutableLogEvent mutableLogEvent = (MutableLogEvent) logEvent;
            mutableLogEvent.clear();
            mutableLogEvent.reserved = false;
        }
    }
}

⏎ org/apache/logging/log4j/core/impl/ReusableLogEventFactory.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
Download 

⇒ Source Code for Apache Log4j JDK Logging Adapter

⇐ Source Code for Apache Log4j API

⇑ Downloading and Reviewing Apache Log4j Packages

⇑⇑ FAQ for Apache Log4j