Source Code for Apache Log4j Core Implementation

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 and source package like You can download them at Apache Log4j Website.

You can also browse Source Code files for Apache Log4j Core Implementation 2.14.1 below.



 * 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
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the license for the specific language governing permissions and
 * limitations under the license.

package org.apache.logging.log4j.core.pattern;

import java.util.List;

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.plugins.Plugin;
import org.apache.logging.log4j.core.layout.PatternLayout;
import org.apache.logging.log4j.util.PerformanceSensitive;

 * Max length pattern converter. Limit contained text to a maximum length.
 * On invalid length the default value 100 is used (and an error message is logged).
 * If max length is greater than 20, an abbreviated text will get ellipsis ("...") appended.
 * Example usage (for email subject):
 * {@code "%maxLen{[AppName, ${hostName}, ${web:contextPath}] %p: %c{1} - %m%notEmpty{ =>%ex{short}}}{160}"}
 * @author Thies Wellpott
@Plugin(name = "maxLength", category = PatternConverter.CATEGORY)
@ConverterKeys({"maxLength", "maxLen"})
public final class MaxLengthConverter extends LogEventPatternConverter {

     * Gets an instance of the class.
     * @param config  The current Configuration.
     * @param options pattern options, an array of two elements: pattern, max length (defaults to 100 on invalid value).
     * @return instance of class.
    public static MaxLengthConverter newInstance(final Configuration config, final String[] options) {
        if (options.length != 2) {
            LOGGER.error("Incorrect number of options on maxLength: expected 2 received {}: {}", options.length,
            return null;
        if (options[0] == null) {
            LOGGER.error("No pattern supplied on maxLength");
            return null;
        if (options[1] == null) {
            LOGGER.error("No length supplied on maxLength");
            return null;
        final PatternParser parser = PatternLayout.createPatternParser(config);
        final List<PatternFormatter> formatters = parser.parse(options[0]);
        return new MaxLengthConverter(formatters, AbstractAppender.parseInt(options[1], 100));

    private final List<PatternFormatter> formatters;
    private final int maxLength;

     * Construct the converter.
     * @param formatters The PatternFormatters to generate the text to manipulate.
     * @param maxLength  The max. length of the resulting string. Ellipsis ("...") is appended on shorted string, if greater than 20.
    private MaxLengthConverter(final List<PatternFormatter> formatters, final int maxLength) {
        super("MaxLength", "maxLength");
        this.maxLength = maxLength;
        this.formatters = formatters;
        LOGGER.trace("new MaxLengthConverter with {}", maxLength);

    public void format(final LogEvent event, final StringBuilder toAppendTo) {
        final int initialLength = toAppendTo.length();
        for (int i = 0; i < formatters.size(); i++) {
            final PatternFormatter formatter = formatters.get(i);
            formatter.format(event, toAppendTo);
            if (toAppendTo.length() > initialLength + maxLength) {        // stop early
        if (toAppendTo.length() > initialLength + maxLength) {
            toAppendTo.setLength(initialLength + maxLength);
            if (maxLength > 20) {        // only append ellipses if length is not very short



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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