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/mom/kafka/KafkaAppender.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.mom.kafka;

import java.io.Serializable;
import java.util.Objects;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

import org.apache.logging.log4j.core.AbstractLifeCycle;
import org.apache.logging.log4j.core.Appender;
import org.apache.logging.log4j.core.Filter;
import org.apache.logging.log4j.core.Layout;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.appender.AbstractAppender;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.Node;
import org.apache.logging.log4j.core.config.Property;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
import org.apache.logging.log4j.core.layout.SerializedLayout;

/**
 * Sends log events to an Apache Kafka topic.
 */
@Plugin(name = "Kafka", category = Node.CATEGORY, elementType = Appender.ELEMENT_TYPE, printObject = true)
public final class KafkaAppender extends AbstractAppender {

	private final Integer retryCount;

	/**
	 * Builds KafkaAppender instances.
	 * 
	 * @param <B> The type to build
	 */
	public static class Builder<B extends Builder<B>> extends AbstractAppender.Builder<B>
			implements org.apache.logging.log4j.core.util.Builder<KafkaAppender> {

		@PluginAttribute("retryCount")
		private String retryCount;

		@PluginAttribute("topic")
		private String topic;

		@PluginAttribute("key")
		private String key;

		@PluginAttribute(value = "syncSend", defaultBoolean = true)
		private boolean syncSend;

		@SuppressWarnings("resource")
		@Override
		public KafkaAppender build() {
			final Layout<? extends Serializable> layout = getLayout();
			if (layout == null) {
				AbstractLifeCycle.LOGGER.error("No layout provided for KafkaAppender");
				return null;
			}
			final KafkaManager kafkaManager = KafkaManager.getManager(getConfiguration().getLoggerContext(), getName(),
					topic, syncSend, getPropertyArray(), key);
			return new KafkaAppender(getName(), layout, getFilter(), isIgnoreExceptions(), kafkaManager,
					getPropertyArray(), getRetryCount());
		}

		public String getTopic() {
			return topic;
		}

		public boolean isSyncSend() {
			return syncSend;
		}

		public B setTopic(final String topic) {
			this.topic = topic;
			return asBuilder();
		}

		public B setSyncSend(final boolean syncSend) {
			this.syncSend = syncSend;
			return asBuilder();
		}

		public B setKey(final String key) {
			this.key = key;
			return asBuilder();
		}

		public Integer getRetryCount() {
			Integer intRetryCount = null;
			try {
				intRetryCount = Integer.valueOf(retryCount);
			} catch (NumberFormatException e) {

			}
			return intRetryCount;

		}

	}

	@Deprecated
	public static KafkaAppender createAppender(final Layout<? extends Serializable> layout, final Filter filter,
			final String name, final boolean ignoreExceptions, final String topic, final Property[] properties,
            final Configuration configuration,
            final String key) {

		if (layout == null) {
			AbstractLifeCycle.LOGGER.error("No layout provided for KafkaAppender");
			return null;
		}
		final KafkaManager kafkaManager = KafkaManager.getManager(configuration.getLoggerContext(), name, topic, true,
				properties, key);
		return new KafkaAppender(name, layout, filter, ignoreExceptions, kafkaManager, null, null);
	}

	/**
	 * Creates a builder for a KafkaAppender.
	 * 
	 * @return a builder for a KafkaAppender.
	 */
	@PluginBuilderFactory
	public static <B extends Builder<B>> B newBuilder() {
		return new Builder<B>().asBuilder();
	}

	private final KafkaManager manager;

	private KafkaAppender(final String name, final Layout<? extends Serializable> layout, final Filter filter,
			final boolean ignoreExceptions, final KafkaManager manager, final Property[] properties,
			final Integer retryCount) {
		super(name, filter, layout, ignoreExceptions, properties);
		this.manager = Objects.requireNonNull(manager, "manager");
		this.retryCount = retryCount;
	}

	@Override
	public void append(final LogEvent event) {
		if (event.getLoggerName() != null && event.getLoggerName().startsWith("org.apache.kafka")) {
			LOGGER.warn("Recursive logging from [{}] for appender [{}].", event.getLoggerName(), getName());
		} else {
			try {
				tryAppend(event);
			} catch (final Exception e) {

				if (this.retryCount != null) {
					int currentRetryAttempt = 0;
					while (currentRetryAttempt < this.retryCount) {
						currentRetryAttempt++;
						try {
							tryAppend(event);
							break;
						} catch (Exception e1) {

						}
					}
				}
				error("Unable to write to Kafka in appender [" + getName() + "]", event, e);
			}
		}
	}

	private void tryAppend(final LogEvent event) throws ExecutionException, InterruptedException, TimeoutException {
		final Layout<? extends Serializable> layout = getLayout();
		byte[] data;
		if (layout instanceof SerializedLayout) {
			final byte[] header = layout.getHeader();
			final byte[] body = layout.toByteArray(event);
			data = new byte[header.length + body.length];
			System.arraycopy(header, 0, data, 0, header.length);
			System.arraycopy(body, 0, data, header.length, body.length);
		} else {
			data = layout.toByteArray(event);
		}
		manager.send(data);
	}

	@Override
	public void start() {
		super.start();
		manager.startup();
	}

	@Override
	public boolean stop(final long timeout, final TimeUnit timeUnit) {
		setStopping();
		boolean stopped = super.stop(timeout, timeUnit, false);
		stopped &= manager.stop(timeout, timeUnit);
		setStopped();
		return stopped;
	}

	@Override
	public String toString() {
		return "KafkaAppender{" + "name=" + getName() + ", state=" + getState() + ", topic=" + manager.getTopic() + '}';
	}
}

⏎ org/apache/logging/log4j/core/appender/mom/kafka/KafkaAppender.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
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