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/rolling/FileExtension.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.rolling;

import java.io.File;
import java.util.Objects;

import org.apache.logging.log4j.core.appender.rolling.action.Action;
import org.apache.logging.log4j.core.appender.rolling.action.CommonsCompressAction;
import org.apache.logging.log4j.core.appender.rolling.action.GzCompressAction;
import org.apache.logging.log4j.core.appender.rolling.action.ZipCompressAction;

/**
 *  Enumerates over supported file extensions for compression.
 */
public enum FileExtension {
    ZIP(".zip") {
        @Override
        Action createCompressAction(final String renameTo, final String compressedName, final boolean deleteSource,
                                    final int compressionLevel) {
            return new ZipCompressAction(source(renameTo), target(compressedName), deleteSource, compressionLevel);
        }
    },
    GZ(".gz") {
        @Override
        Action createCompressAction(final String renameTo, final String compressedName, final boolean deleteSource,
                                    final int compressionLevel) {
            return new GzCompressAction(source(renameTo), target(compressedName), deleteSource, compressionLevel);
        }
    },
    BZIP2(".bz2") {
        @Override
        Action createCompressAction(final String renameTo, final String compressedName, final boolean deleteSource,
                                    final int compressionLevel) {
            // One of "gz", "bzip2", "xz", "pack200", or "deflate".
            return new CommonsCompressAction("bzip2", source(renameTo), target(compressedName), deleteSource);
        }
    },
    DEFLATE(".deflate") {
        @Override
        Action createCompressAction(final String renameTo, final String compressedName, final boolean deleteSource,
                                    final int compressionLevel) {
            // One of "gz", "bzip2", "xz", "pack200", or "deflate".
            return new CommonsCompressAction("deflate", source(renameTo), target(compressedName), deleteSource);
        }
    },
    PACK200(".pack200") {
        @Override
        Action createCompressAction(final String renameTo, final String compressedName, final boolean deleteSource,
                                    final int compressionLevel) {
            // One of "gz", "bzip2", "xz", "pack200", or "deflate".
            return new CommonsCompressAction("pack200", source(renameTo), target(compressedName), deleteSource);
        }
    },
    XZ(".xz") {
        @Override
        Action createCompressAction(final String renameTo, final String compressedName, final boolean deleteSource,
                                    final int compressionLevel) {
            // One of "gz", "bzip2", "xz", "pack200", or "deflate".
            return new CommonsCompressAction("xz", source(renameTo), target(compressedName), deleteSource);
        }
    };

    public static FileExtension lookup(final String fileExtension) {
        for (final FileExtension ext : values()) {
            if (ext.isExtensionFor(fileExtension)) {
                return ext;
            }
        }
        return null;
    }

    public static FileExtension lookupForFile(final String fileName) {
        for (final FileExtension ext : values()) {
            if (fileName.endsWith(ext.extension)) {
                return ext;
            }
        }
        return null;
    }

    private final String extension;

    private FileExtension(final String extension) {
        Objects.requireNonNull(extension, "extension");
        this.extension = extension;
    }

    abstract Action createCompressAction(String renameTo, String compressedName, boolean deleteSource,
                                         int compressionLevel);

    String getExtension() {
        return extension;
    }

    boolean isExtensionFor(final String s) {
        return s.endsWith(this.extension);
    }

    int length() {
        return extension.length();
    }

    File source(final String fileName) {
        return new File(fileName);
    }

    File target(final String fileName) {
        return new File(fileName);
    }
}

⏎ org/apache/logging/log4j/core/appender/rolling/FileExtension.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