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/appender/MemoryMappedFileManager.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.appender;

import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.io.Serializable;
import java.lang.reflect.Method;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.AccessController;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;

import org.apache.logging.log4j.core.Layout;
import org.apache.logging.log4j.core.util.Closer;
import org.apache.logging.log4j.core.util.FileUtils;
import org.apache.logging.log4j.core.util.NullOutputStream;

//Lines too long...
//CHECKSTYLE:OFF
/**
 * Extends OutputStreamManager but instead of using a buffered output stream, this class maps a region of a file into
 * memory and writes to this memory region.
 * <p>
 *
 * @see <a href="http://www.codeproject.com/Tips/683614/Things-to-Know-about-Memory-Mapped-File-in-Java">
 *      http://www.codeproject.com/Tips/683614/Things-to-Know-about-Memory-Mapped-File-in-Java</a>
 * @see <a href="http://bugs.java.com/view_bug.do?bug_id=6893654">http://bugs.java.com/view_bug.do?bug_id=6893654</a>
 * @see <a href="http://bugs.java.com/view_bug.do?bug_id=4724038">http://bugs.java.com/view_bug.do?bug_id=4724038</a>
 * @see <a
 *      href="http://stackoverflow.com/questions/9261316/memory-mapped-mappedbytebuffer-or-direct-bytebuffer-for-db-implementation">
 *      http://stackoverflow.com/questions/9261316/memory-mapped-mappedbytebuffer-or-direct-bytebuffer-for-db-implementation</a>
 *
 * @since 2.1
 */
//CHECKSTYLE:ON
public class MemoryMappedFileManager extends OutputStreamManager {
    /**
     * Default length of region to map.
     */
    static final int DEFAULT_REGION_LENGTH = 32 * 1024 * 1024;
    private static final int MAX_REMAP_COUNT = 10;
    private static final MemoryMappedFileManagerFactory FACTORY = new MemoryMappedFileManagerFactory();
    private static final double NANOS_PER_MILLISEC = 1000.0 * 1000.0;

    private final boolean immediateFlush;
    private final int regionLength;
    private final String advertiseURI;
    private final RandomAccessFile randomAccessFile;
    private final ThreadLocal<Boolean> isEndOfBatch = new ThreadLocal<>();
    private MappedByteBuffer mappedBuffer;
    private long mappingOffset;

    protected MemoryMappedFileManager(final RandomAccessFile file, final String fileName, final OutputStream os,
            final boolean immediateFlush, final long position, final int regionLength, final String advertiseURI,
            final Layout<? extends Serializable> layout, final boolean writeHeader) throws IOException {
        super(os, fileName, layout, writeHeader, ByteBuffer.wrap(new byte[0]));
        this.immediateFlush = immediateFlush;
        this.randomAccessFile = Objects.requireNonNull(file, "RandomAccessFile");
        this.regionLength = regionLength;
        this.advertiseURI = advertiseURI;
        this.isEndOfBatch.set(Boolean.FALSE);
        this.mappedBuffer = mmap(randomAccessFile.getChannel(), getFileName(), position, regionLength);
        this.byteBuffer = mappedBuffer;
        this.mappingOffset = position;
    }

    /**
     * Returns the MemoryMappedFileManager.
     *
     * @param fileName The name of the file to manage.
     * @param append true if the file should be appended to, false if it should be overwritten.
     * @param immediateFlush true if the contents should be flushed to disk on every write
     * @param regionLength The mapped region length.
     * @param advertiseURI the URI to use when advertising the file
     * @param layout The layout.
     * @return A MemoryMappedFileManager for the File.
     */
    public static MemoryMappedFileManager getFileManager(final String fileName, final boolean append,
            final boolean immediateFlush, final int regionLength, final String advertiseURI,
            final Layout<? extends Serializable> layout) {
        return narrow(MemoryMappedFileManager.class, getManager(fileName, new FactoryData(append, immediateFlush,
                regionLength, advertiseURI, layout), FACTORY));
    }

    public Boolean isEndOfBatch() {
        return isEndOfBatch.get();
    }

    public void setEndOfBatch(final boolean endOfBatch) {
        this.isEndOfBatch.set(Boolean.valueOf(endOfBatch));
    }

    @Override
    protected synchronized void write(final byte[] bytes, int offset, int length, final boolean immediateFlush) {
        while (length > mappedBuffer.remaining()) {
            final int chunk = mappedBuffer.remaining();
            mappedBuffer.put(bytes, offset, chunk);
            offset += chunk;
            length -= chunk;
            remap();
        }
        mappedBuffer.put(bytes, offset, length);

        // no need to call flush() if force is true,
        // already done in AbstractOutputStreamAppender.append
    }

    private synchronized void remap() {
        final long offset = this.mappingOffset + mappedBuffer.position();
        final int length = mappedBuffer.remaining() + regionLength;
        try {
            unsafeUnmap(mappedBuffer);
            final long fileLength = randomAccessFile.length() + regionLength;
            LOGGER.debug("{} {} extending {} by {} bytes to {}", getClass().getSimpleName(), getName(), getFileName(),
                    regionLength, fileLength);

            final long startNanos = System.nanoTime();
            randomAccessFile.setLength(fileLength);
            final float millis = (float) ((System.nanoTime() - startNanos) / NANOS_PER_MILLISEC);
            LOGGER.debug("{} {} extended {} OK in {} millis", getClass().getSimpleName(), getName(), getFileName(),
                    millis);

            mappedBuffer = mmap(randomAccessFile.getChannel(), getFileName(), offset, length);
            this.byteBuffer = mappedBuffer;
            mappingOffset = offset;
        } catch (final Exception ex) {
            logError("Unable to remap", ex);
        }
    }

    @Override
    public synchronized void flush() {
        mappedBuffer.force();
    }

    @Override
    public synchronized boolean closeOutputStream() {
        final long position = mappedBuffer.position();
        final long length = mappingOffset + position;
        try {
            unsafeUnmap(mappedBuffer);
        } catch (final Exception ex) {
            logError("Unable to unmap MappedBuffer", ex);
        }
        try {
            LOGGER.debug("MMapAppender closing. Setting {} length to {} (offset {} + position {})", getFileName(),
                    length, mappingOffset, position);
            randomAccessFile.setLength(length);
            randomAccessFile.close();
            return true;
        } catch (final IOException ex) {
            logError("Unable to close MemoryMappedFile", ex);
            return false;
        }
    }

    public static MappedByteBuffer mmap(final FileChannel fileChannel, final String fileName, final long start,
            final int size) throws IOException {
        for (int i = 1;; i++) {
            try {
                LOGGER.debug("MMapAppender remapping {} start={}, size={}", fileName, start, size);

                final long startNanos = System.nanoTime();
                final MappedByteBuffer map = fileChannel.map(FileChannel.MapMode.READ_WRITE, start, size);
                map.order(ByteOrder.nativeOrder());

                final float millis = (float) ((System.nanoTime() - startNanos) / NANOS_PER_MILLISEC);
                LOGGER.debug("MMapAppender remapped {} OK in {} millis", fileName, millis);

                return map;
            } catch (final IOException e) {
                if (e.getMessage() == null || !e.getMessage().endsWith("user-mapped section open")) {
                    throw e;
                }
                LOGGER.debug("Remap attempt {}/{} failed. Retrying...", i, MAX_REMAP_COUNT, e);
                if (i < MAX_REMAP_COUNT) {
                    Thread.yield();
                } else {
                    try {
                        Thread.sleep(1);
                    } catch (final InterruptedException ignored) {
                        Thread.currentThread().interrupt();
                        throw e;
                    }
                }
            }
        }
    }

    private static void unsafeUnmap(final MappedByteBuffer mbb) throws PrivilegedActionException {
        LOGGER.debug("MMapAppender unmapping old buffer...");
        final long startNanos = System.nanoTime();
        AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
            final Method getCleanerMethod = mbb.getClass().getMethod("cleaner");
            getCleanerMethod.setAccessible(true);
            final Object cleaner = getCleanerMethod.invoke(mbb); // sun.misc.Cleaner instance
            final Method cleanMethod = cleaner.getClass().getMethod("clean");
            cleanMethod.invoke(cleaner);
            return null;
        });
        final float millis = (float) ((System.nanoTime() - startNanos) / NANOS_PER_MILLISEC);
        LOGGER.debug("MMapAppender unmapped buffer OK in {} millis", millis);
    }

    /**
     * Returns the name of the File being managed.
     *
     * @return The name of the File being managed.
     */
    public String getFileName() {
        return getName();
    }

    /**
     * Returns the length of the memory mapped region.
     *
     * @return the length of the mapped region
     */
    public int getRegionLength() {
        return regionLength;
    }

    /**
     * Returns {@code true} if the content of the buffer should be forced to the storage device on every write,
     * {@code false} otherwise.
     *
     * @return whether each write should be force-sync'ed
     */
    public boolean isImmediateFlush() {
        return immediateFlush;
    }

    /**
     * Gets this FileManager's content format specified by:
     * <p>
     * Key: "fileURI" Value: provided "advertiseURI" param.
     * </p>
     *
     * @return Map of content format keys supporting FileManager
     */
    @Override
    public Map<String, String> getContentFormat() {
        final Map<String, String> result = new HashMap<>(super.getContentFormat());
        result.put("fileURI", advertiseURI);
        return result;
    }

    @Override
    protected void flushBuffer(final ByteBuffer buffer) {
        // do nothing (do not call drain() to avoid spurious remapping)
    }

    @Override
    public ByteBuffer getByteBuffer() {
        return mappedBuffer;
    }

    @Override
    public ByteBuffer drain(final ByteBuffer buf) {
        remap();
        return mappedBuffer;
    }

    /**
     * Factory Data.
     */
    private static class FactoryData {
        private final boolean append;
        private final boolean immediateFlush;
        private final int regionLength;
        private final String advertiseURI;
        private final Layout<? extends Serializable> layout;

        /**
         * Constructor.
         *
         * @param append Append to existing file or truncate.
         * @param immediateFlush forces the memory content to be written to the storage device on every event
         * @param regionLength length of the mapped region
         * @param advertiseURI the URI to use when advertising the file
         * @param layout The layout.
         */
        public FactoryData(final boolean append, final boolean immediateFlush, final int regionLength,
                final String advertiseURI, final Layout<? extends Serializable> layout) {
            this.append = append;
            this.immediateFlush = immediateFlush;
            this.regionLength = regionLength;
            this.advertiseURI = advertiseURI;
            this.layout = layout;
        }
    }

    /**
     * Factory to create a MemoryMappedFileManager.
     */
    private static class MemoryMappedFileManagerFactory
            implements ManagerFactory<MemoryMappedFileManager, FactoryData> {

        /**
         * Create a MemoryMappedFileManager.
         *
         * @param name The name of the File.
         * @param data The FactoryData
         * @return The MemoryMappedFileManager for the File.
         */
        @SuppressWarnings("resource")
        @Override
        public MemoryMappedFileManager createManager(final String name, final FactoryData data) {
            final File file = new File(name);
            if (!data.append) {
                file.delete();
            }

            final boolean writeHeader = !data.append || !file.exists();
            final OutputStream os = NullOutputStream.getInstance();
            RandomAccessFile raf = null;
            try {
                FileUtils.makeParentDirs(file);
                raf = new RandomAccessFile(name, "rw");
                final long position = (data.append) ? raf.length() : 0;
                raf.setLength(position + data.regionLength);
                return new MemoryMappedFileManager(raf, name, os, data.immediateFlush, position, data.regionLength,
                        data.advertiseURI, data.layout, writeHeader);
            } catch (final Exception ex) {
                LOGGER.error("MemoryMappedFileManager (" + name + ") " + ex, ex);
                Closer.closeSilently(raf);
            }
            return null;
        }
    }
}

⏎ org/apache/logging/log4j/core/appender/MemoryMappedFileManager.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