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/lookup/DateLookup.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.lookup;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.Marker;
import org.apache.logging.log4j.MarkerManager;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.status.StatusLogger;

/**
 * Formats the current date or the date in the LogEvent. The "key" is used as the format String.
 */
@Plugin(name = "date", category = StrLookup.CATEGORY)
public class DateLookup implements StrLookup {

    private static final Logger LOGGER = StatusLogger.getLogger();
    private static final Marker LOOKUP = MarkerManager.getMarker("LOOKUP");

    /**
     * Looks up the value of the environment variable.
     * @param key the format to use. If null, the default DateFormat will be used.
     * @return The value of the environment variable.
     */
    @Override
    public String lookup(final String key) {
        return formatDate(System.currentTimeMillis(), key);
    }

    /**
     * Looks up the value of the environment variable.
     * @param event The current LogEvent (is ignored by this StrLookup).
     * @param key the format to use. If null, the default DateFormat will be used.
     * @return The value of the environment variable.
     */
    @Override
    public String lookup(final LogEvent event, final String key) {
        return formatDate(event.getTimeMillis(), key);
    }

    private String formatDate(final long date, final String format) {
        DateFormat dateFormat = null;
        if (format != null) {
            try {
                dateFormat = new SimpleDateFormat(format);
            } catch (final Exception ex) {
                LOGGER.error(LOOKUP, "Invalid date format: [{}], using default", format, ex);
            }
        }
        if (dateFormat == null) {
            dateFormat = DateFormat.getInstance();
        }
        return dateFormat.format(new Date(date));
    }
}

⏎ org/apache/logging/log4j/core/lookup/DateLookup.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