Source Code for Apache Log4j Core Implementation

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 and source package like You can download them at Apache Log4j Website.

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



 * 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
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the license for the specific language governing permissions and
 * limitations under the license.
package org.apache.logging.log4j.core.layout;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CodingErrorAction;
import java.util.Objects;

import org.apache.logging.log4j.core.util.Constants;
import org.apache.logging.log4j.status.StatusLogger;

 * Encoder for StringBuilders that uses ThreadLocals to avoid locking as much as possible.
public class StringBuilderEncoder implements Encoder<StringBuilder> {

    private static final int DEFAULT_BYTE_BUFFER_SIZE = 8 * 1024;
     * This ThreadLocal uses raw and inconvenient Object[] to store three heterogeneous objects (CharEncoder, CharBuffer
     * and ByteBuffer) instead of a custom class, because it needs to contain JDK classes, no custom (Log4j) classes.
     * Where possible putting only JDK classes in ThreadLocals is preferable to avoid memory leaks in web containers:
     * the Log4j classes may be loaded by a separate class loader which cannot be garbage collected if a thread pool
     * threadlocal still has a reference to it.
     * Using just one ThreadLocal instead of three separate ones is an optimization: {@link ThreadLocal.ThreadLocalMap}
     * is polluted less, {@link ThreadLocal.ThreadLocalMap#get()} is called only once on each call to {@link #encode}
     * instead of three times.
    private final ThreadLocal<Object[]> threadLocal = new ThreadLocal<>();
    private final Charset charset;
    private final int charBufferSize;
    private final int byteBufferSize;

    public StringBuilderEncoder(final Charset charset) {

    public StringBuilderEncoder(final Charset charset, final int charBufferSize, final int byteBufferSize) {
        this.charBufferSize = charBufferSize;
        this.byteBufferSize = byteBufferSize;
        this.charset = Objects.requireNonNull(charset, "charset");

    public void encode(final StringBuilder source, final ByteBufferDestination destination) {
        try {
            final Object[] threadLocalState = getThreadLocalState();
            final CharsetEncoder charsetEncoder = (CharsetEncoder) threadLocalState[0];
            final CharBuffer charBuffer = (CharBuffer) threadLocalState[1];
            final ByteBuffer byteBuffer = (ByteBuffer) threadLocalState[2];
            TextEncoderHelper.encodeText(charsetEncoder, charBuffer, byteBuffer, source, destination);
        } catch (final Exception ex) {
            logEncodeTextException(ex, source, destination);
            TextEncoderHelper.encodeTextFallBack(charset, source, destination);

    private Object[] getThreadLocalState() {
        Object[] threadLocalState = threadLocal.get();
        if (threadLocalState == null) {
            threadLocalState = new Object[] {
        } else {
            ((CharsetEncoder) threadLocalState[0]).reset();
            ((CharBuffer) threadLocalState[1]).clear();
            ((ByteBuffer) threadLocalState[2]).clear();
        return threadLocalState;

    private void logEncodeTextException(final Exception ex, final StringBuilder text,
            final ByteBufferDestination destination) {
        StatusLogger.getLogger().error("Recovering from StringBuilderEncoder.encode('{}') error: {}", text, ex, ex);



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


Source Code for Apache Log4j JDK Logging Adapter

Source Code for Apache Log4j API

Downloading and Reviewing Apache Log4j Packages

⇑⇑ FAQ for Apache Log4j

2015-11-03, 83840👍, 0💬