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/pattern/MdcPatternConverter.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.pattern;

import org.apache.logging.log4j.util.PerformanceSensitive;
import org.apache.logging.log4j.util.ReadOnlyStringMap;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.util.TriConsumer;
import org.apache.logging.log4j.util.StringBuilders;

/**
 * Able to handle the contents of the LogEvent's MDC and either
 * output the entire contents of the properties in a similar format to the
 * java.util.Hashtable.toString(), or to output the value of a specific key
 * within the property bundle
 * when this pattern converter has the option set.
 */
@Plugin(name = "MdcPatternConverter", category = PatternConverter.CATEGORY)
@ConverterKeys({ "X", "mdc", "MDC" })
@PerformanceSensitive("allocation")
public final class MdcPatternConverter extends LogEventPatternConverter {

    /**
     * Name of property to output.
     */
    private final String key;
    private final String[] keys;
    private final boolean full;

    /**
     * Private constructor.
     *
     * @param options options, may be null.
     */
    private MdcPatternConverter(final String[] options) {
        super(options != null && options.length > 0 ? "MDC{" + options[0] + '}' : "MDC", "mdc");
        if (options != null && options.length > 0) {
            full = false;
            if (options[0].indexOf(',') > 0) {
                keys = options[0].split(",");
                for (int i = 0; i < keys.length; i++) {
                    keys[i] = keys[i].trim();
                }
                key = null;
            } else {
                keys = null;
                key = options[0];
            }
        } else {
            full = true;
            key = null;
            keys = null;
        }
    }

    /**
     * Obtains an instance of PropertiesPatternConverter.
     *
     * @param options options, may be null or first element contains name of property to format.
     * @return instance of PropertiesPatternConverter.
     */
    public static MdcPatternConverter newInstance(final String[] options) {
        return new MdcPatternConverter(options);
    }

    private static final TriConsumer<String, Object, StringBuilder> WRITE_KEY_VALUES_INTO = (key, value, sb) -> {
        sb.append(key).append('=');
        StringBuilders.appendValue(sb, value);
        sb.append(", ");
    };

    /**
     * {@inheritDoc}
     */
    @Override
    public void format(final LogEvent event, final StringBuilder toAppendTo) {
        final ReadOnlyStringMap contextData = event.getContextData();
        // if there is no additional options, we output every single
        // Key/Value pair for the MDC in a similar format to Hashtable.toString()
        if (full) {
            if (contextData == null || contextData.isEmpty()) {
                toAppendTo.append("{}");
                return;
            }
            appendFully(contextData, toAppendTo);
        } else if (keys != null) {
            if (contextData == null || contextData.isEmpty()) {
                toAppendTo.append("{}");
                return;
            }
            appendSelectedKeys(keys, contextData, toAppendTo);
        } else if (contextData != null){
            // otherwise they just want a single key output
            final Object value = contextData.getValue(key);
            if (value != null) {
                StringBuilders.appendValue(toAppendTo, value);
            }
        }
    }

    private static void appendFully(final ReadOnlyStringMap contextData, final StringBuilder toAppendTo) {
        toAppendTo.append("{");
        final int start = toAppendTo.length();
        contextData.forEach(WRITE_KEY_VALUES_INTO, toAppendTo);
        final int end = toAppendTo.length();
        if (end > start) {
            toAppendTo.setCharAt(end - 2, '}');
            toAppendTo.deleteCharAt(end - 1);
        } else {
            toAppendTo.append('}');
        }
    }

    private static void appendSelectedKeys(final String[] keys, final ReadOnlyStringMap contextData, final StringBuilder sb) {
        // Print all the keys in the array that have a value.
        final int start = sb.length();
        sb.append('{');
        for (int i = 0; i < keys.length; i++) {
            final String theKey = keys[i];
            final Object value = contextData.getValue(theKey);
            if (value != null) { // !contextData.containskey(theKey)
                if (sb.length() - start > 1) {
                    sb.append(", ");
                }
                sb.append(theKey).append('=');
                StringBuilders.appendValue(sb, value);
            }
        }
        sb.append('}');
    }
}

⏎ org/apache/logging/log4j/core/pattern/MdcPatternConverter.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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