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/Layout.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;

import java.io.Serializable;
import java.util.Map;

import org.apache.logging.log4j.core.layout.ByteBufferDestination;
import org.apache.logging.log4j.core.layout.Encoder;

/**
 * Lays out a {@linkplain LogEvent} in different formats.
 *
 * The formats are:
 * <ul>
 * <li>
 * {@code byte[]}</li>
 * <li>
 * an implementer of {@linkplain Serializable}, like {@code byte[]}</li>
 * <li>
 * {@linkplain String}</li>
 * <li>
 * {@linkplain LogEvent}</li>
 * </ul>
 * <p>
 * Since 2.6, Layouts can {@linkplain Encoder#encode(Object, ByteBufferDestination) encode} a {@code LogEvent} directly
 * to a {@link ByteBufferDestination} without creating temporary intermediary objects.
 * </p>
 *
 * @param <T>
 *            The {@link Serializable} type returned by {@link #toSerializable(LogEvent)}
 */
public interface Layout<T extends Serializable> extends Encoder<LogEvent> {

    /**
     * Main {@linkplain org.apache.logging.log4j.core.config.plugins.Plugin#elementType() plugin element type} for
     * Layout plugins.
     *
     * @since 2.1
     */
    String ELEMENT_TYPE = "layout";

    /**
     * Returns the format for the layout format.
     * @return The footer.
     */
    byte[] getFooter();

    /**
     * Returns the header for the layout format.
     * @return The header.
     */
    byte[] getHeader();

    /**
     * Formats the event suitable for display.
     *
     * @param event The Logging Event.
     * @return The formatted event.
     */
    byte[] toByteArray(LogEvent event);

    /**
     * Formats the event as an Object that can be serialized.
     *
     * @param event The Logging Event.
     * @return The formatted event.
     */
    T toSerializable(LogEvent event);

    /**
     * Returns the content type output by this layout. The base class returns "text/plain".
     *
     * @return the content type.
     */
    String getContentType();

    /**
     * Returns a description of the content format.
     *
     * @return a Map of key/value pairs describing the Layout-specific content format, or an empty Map if no content
     * format descriptors are specified.
     */
    Map<String, String> getContentFormat();
}

⏎ org/apache/logging/log4j/core/Layout.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