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/util/Transform.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.util;

import org.apache.logging.log4j.util.Strings;


/**
 * Utility class for transforming strings.
 */
public final class Transform {

    private static final String CDATA_START = "<![CDATA[";
    private static final String CDATA_END = "]]>";
    private static final String CDATA_PSEUDO_END = "]]&gt;";
    private static final String CDATA_EMBEDED_END = CDATA_END + CDATA_PSEUDO_END + CDATA_START;
    private static final int CDATA_END_LEN = CDATA_END.length();

    private Transform() {
    }

    /**
     * This method takes a string which may contain HTML tags (ie,
     * &lt;b&gt;, &lt;table&gt;, etc) and replaces any
     * '&lt;',  '&gt;' , '&amp;' or '&quot;'
     * characters with respective predefined entity references.
     *
     * @param input The text to be converted.
     * @return The input string with the special characters replaced.
     */
    public static String escapeHtmlTags(final String input) {
        // Check if the string is null, zero length or devoid of special characters
        // if so, return what was sent in.

        if (Strings.isEmpty(input)
            || (input.indexOf('"') == -1 &&
            input.indexOf('&') == -1 &&
            input.indexOf('<') == -1 &&
            input.indexOf('>') == -1)) {
            return input;
        }

        //Use a StringBuilder in lieu of String concatenation -- it is
        //much more efficient this way.

        final StringBuilder buf = new StringBuilder(input.length() + 6);

        final int len = input.length();
        for (int i = 0; i < len; i++) {
            final char ch = input.charAt(i);
            if (ch > '>') {
                buf.append(ch);
            } else
                switch (ch) {
                case '<':
                    buf.append("&lt;");
                    break;
                case '>':
                    buf.append("&gt;");
                    break;
                case '&':
                    buf.append("&amp;");
                    break;
                case '"':
                    buf.append("&quot;");
                    break;
                default:
                    buf.append(ch);
                    break;
                }
        }
        return buf.toString();
    }

    /**
     * Ensures that embedded CDEnd strings (]]&gt;) are handled properly
     * within message, NDC and throwable tag text.
     *
     * @param buf StringBuilder holding the XML data to this point.  The
     *            initial CDStart (&lt;![CDATA[) and final CDEnd (]]&gt;) of the CDATA
     *            section are the responsibility of the calling method.
     * @param str The String that is inserted into an existing CDATA Section within buf.
     */
    public static void appendEscapingCData(final StringBuilder buf, final String str) {
        if (str != null) {
            int end = str.indexOf(CDATA_END);
            if (end < 0) {
                buf.append(str);
            } else {
                int start = 0;
                while (end > -1) {
                    buf.append(str.substring(start, end));
                    buf.append(CDATA_EMBEDED_END);
                    start = end + CDATA_END_LEN;
                    if (start < str.length()) {
                        end = str.indexOf(CDATA_END, start);
                    } else {
                        return;
                    }
                }
                buf.append(str.substring(start));
            }
        }
    }

    /**
     * This method takes a string which may contain JSON reserved chars and
     * escapes them.
     *
     * @param input The text to be converted.
     * @return The input string with the special characters replaced.
     */
    public static String escapeJsonControlCharacters(final String input) {
        // Check if the string is null, zero length or devoid of special characters
        // if so, return what was sent in.

        // TODO: escaped Unicode chars.

        if (Strings.isEmpty(input)
            || (input.indexOf('"') == -1 &&
            input.indexOf('\\') == -1 &&
            input.indexOf('/') == -1 &&
            input.indexOf('\b') == -1 &&
            input.indexOf('\f') == -1 &&
            input.indexOf('\n') == -1 &&
            input.indexOf('\r') == -1 &&
            input.indexOf('\t') == -1)) {
            return input;
        }

        final StringBuilder buf = new StringBuilder(input.length() + 6);

        final int len = input.length();
        for (int i = 0; i < len; i++) {
            final char ch = input.charAt(i);
            final String escBs = "\\";
            switch (ch) {
            case '"':
                buf.append(escBs);
                buf.append(ch);
                break;
            case '\\':
                buf.append(escBs);
                buf.append(ch);
                break;
            case '/':
                buf.append(escBs);
                buf.append(ch);
                break;
            case '\b':
                buf.append(escBs);
                buf.append('b');
                break;
            case '\f':
                buf.append(escBs);
                buf.append('f');
                break;
            case '\n':
                buf.append(escBs);
                buf.append('n');
                break;
            case '\r':
                buf.append(escBs);
                buf.append('r');
                break;
            case '\t':
                buf.append(escBs);
                buf.append('t');
                break;
            default:
                buf.append(ch);
            }
        }
        return buf.toString();
    }
}

⏎ org/apache/logging/log4j/core/util/Transform.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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