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/config/plugins/Plugin.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.config.plugins;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.apache.logging.log4j.util.Strings;

/**
 * Annotation that identifies a Class as a Plugin.
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Plugin {

    /**
     * Value of the elementType when none is specified.
     */
    String EMPTY = Strings.EMPTY;

    /**
     * Name of the plugin. Note that this name is case-insensitive.
     */
    String name();

    /**
     * Category to place the plugin under. Category names are case-sensitive.
     */
    String category();

    /**
     * Name of the corresponding category of elements this plugin belongs under. For example, {@code appender} would
     * indicate an {@link org.apache.logging.log4j.core.Appender} plugin which would be in the
     * {@code <Appenders/>} element of a {@link org.apache.logging.log4j.core.config.Configuration}.
     */
    String elementType() default EMPTY;

    /**
     * Indicates if the plugin class implements a useful {@link Object#toString()} method for use in log messages.
     */
    boolean printObject() default false;

    boolean deferChildren() default false;
}

⏎ org/apache/logging/log4j/core/config/plugins/Plugin.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