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/rewrite/MapRewritePolicy.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.rewrite;

import java.util.HashMap;
import java.util.Map;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.core.Core;
import org.apache.logging.log4j.core.LogEvent;
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.PluginElement;
import org.apache.logging.log4j.core.config.plugins.PluginFactory;
import org.apache.logging.log4j.core.impl.Log4jLogEvent;
import org.apache.logging.log4j.core.util.KeyValuePair;
import org.apache.logging.log4j.message.MapMessage;
import org.apache.logging.log4j.message.Message;
import org.apache.logging.log4j.status.StatusLogger;

/**
 * This policy modifies events by replacing or possibly adding keys and values to the MapMessage.
 */
@Plugin(name = "MapRewritePolicy", category = Core.CATEGORY_NAME, elementType = "rewritePolicy", printObject = true)
public final class MapRewritePolicy implements RewritePolicy {

    /**
     * Allow subclasses access to the status logger without creating another instance.
     */
    protected static final Logger LOGGER = StatusLogger.getLogger();

    private final Map<String, Object> map;

    private final Mode mode;

    private MapRewritePolicy(final Map<String, Object> map, final Mode mode) {
        this.map = map;
        this.mode = mode;
    }

    /**
     * Rewrite the event.
     * @param source a logging event that may be returned or
     * used to create a new logging event.
     * @return The LogEvent after rewriting.
     */
    @Override
    public LogEvent rewrite(final LogEvent source) {
        final Message msg = source.getMessage();
        if (msg == null || !(msg instanceof MapMessage)) {
            return source;
        }

        @SuppressWarnings("unchecked")
        final MapMessage<?, Object> mapMsg = (MapMessage<?, Object>) msg;
        final Map<String, Object> newMap = new HashMap<>(mapMsg.getData());
        switch (mode) {
            case Add: {
                newMap.putAll(map);
                break;
            }
            default: {
                for (final Map.Entry<String, Object> entry : map.entrySet()) {
                    if (newMap.containsKey(entry.getKey())) {
                        newMap.put(entry.getKey(), entry.getValue());
                    }
                }
            }
        }
        final Message message = mapMsg.newInstance(newMap);
        return new Log4jLogEvent.Builder(source).setMessage(message).build();
    }

    /**
     * An enumeration to identify whether keys not in the MapMessage should be added or whether only existing
     * keys should be updated.
     */
    public enum Mode {

        /**
         * Keys should be added.
         */
        Add,

        /**
         * Keys should be updated.
         */
        Update
    }

    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder();
        sb.append("mode=").append(mode);
        sb.append(" {");
        boolean first = true;
        for (final Map.Entry<String, Object> entry : map.entrySet()) {
            if (!first) {
                sb.append(", ");
            }
            sb.append(entry.getKey()).append('=').append(entry.getValue());
            first = false;
        }
        sb.append('}');
        return sb.toString();
    }

    /**
     * The factory method to create the MapRewritePolicy.
     * @param mode The string representation of the Mode.
     * @param pairs key/value pairs for the new Map keys and values.
     * @return The MapRewritePolicy.
     */
    @PluginFactory
    public static MapRewritePolicy createPolicy(
            @PluginAttribute("mode") final String mode,
            @PluginElement("KeyValuePair") final KeyValuePair[] pairs) {
        Mode op = mode == null ? op = Mode.Add : Mode.valueOf(mode);
        if (pairs == null || pairs.length == 0) {
            LOGGER.error("keys and values must be specified for the MapRewritePolicy");
            return null;
        }
        final Map<String, Object> map = new HashMap<>();
        for (final KeyValuePair pair : pairs) {
            final String key = pair.getKey();
            if (key == null) {
                LOGGER.error("A null key is not valid in MapRewritePolicy");
                continue;
            }
            final String value = pair.getValue();
            if (value == null) {
                LOGGER.error("A null value for key " + key + " is not allowed in MapRewritePolicy");
                continue;
            }
            map.put(pair.getKey(), pair.getValue());
        }
        if (map.isEmpty()) {
            LOGGER.error("MapRewritePolicy is not configured with any valid key value pairs");
            return null;
        }
        return new MapRewritePolicy(map, op);
    }
}

⏎ org/apache/logging/log4j/core/appender/rewrite/MapRewritePolicy.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