Apache Log4j JDK Logging Adapter is a custom implementation of java.util.logging.LogManager that uses Log4j. This adapter can be used with either the Log4j API or Log4j Core.

Bytecode (Java 8) for Apache Log4j JDK Logging Adapter is provided in a separate JAR file like log4j-jul-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 JDK Logging Adapter 2.14.1 below.

⏎ org/apache/logging/log4j/jul/ApiLogger.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.jul;

import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.logging.Filter;
import java.util.logging.Level;
import java.util.logging.LogRecord;
import java.util.logging.Logger;

import org.apache.logging.log4j.message.Message;
import org.apache.logging.log4j.message.MessageFactory;
import org.apache.logging.log4j.spi.ExtendedLogger;

/**
 * Log4j API implementation of the JUL {@link Logger} class. <strong>Note that this implementation does
 * <em>not</em> use the {@link java.util.logging.Handler} class.</strong> Instead, logging is delegated to the
 * underlying Log4j {@link org.apache.logging.log4j.Logger} which may be implemented in one of many different ways.
 * Consult the documentation for your Log4j Provider for more details.
 * <p>Note that the methods {@link #getParent()} and {@link #setLevel(java.util.logging.Level)} are not supported by
 * this implementation. If you need support for these methods, then you'll need to use log4j-core. The
 * {@link #getParent()} method will not fail (thanks to JUL API limitations), but it won't necessarily be
 * accurate!</p>
 * <p>Also note that {@link #setParent(java.util.logging.Logger)} is explicitly unsupported. Parent loggers are
 * determined using the syntax of the logger name; not through an arbitrary graph of loggers.</p>
 *
 * @since 2.1
 */
public class ApiLogger extends Logger {

    private final WrappedLogger logger;
    private static final String FQCN = ApiLogger.class.getName();

    ApiLogger(final ExtendedLogger logger) {
        super(logger.getName(), null);
        final Level javaLevel = LevelTranslator.toJavaLevel(logger.getLevel());
        // "java.util.logging.LoggingPermission" "control"
        AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
            ApiLogger.super.setLevel(javaLevel);
            return null;
        });
        this.logger = new WrappedLogger(logger);
    }

    @Override
    public void log(final LogRecord record) {
        if (isFiltered(record)) {
            return;
        }
        final org.apache.logging.log4j.Level level = LevelTranslator.toLevel(record.getLevel());
        final Object[] parameters = record.getParameters();
        final MessageFactory messageFactory = logger.getMessageFactory();
        final Message message = parameters == null ?
            messageFactory.newMessage(record.getMessage()) /* LOG4J2-1251: not formatted case */ :
            messageFactory.newMessage(record.getMessage(), parameters);
        final Throwable thrown = record.getThrown();
        logger.logIfEnabled(FQCN, level, null, message, thrown);
    }

    // support for Logger.getFilter()/Logger.setFilter()
    boolean isFiltered(final LogRecord logRecord) {
        final Filter filter = getFilter();
        return filter != null && !filter.isLoggable(logRecord);
    }

    @Override
    public boolean isLoggable(final Level level) {
        return logger.isEnabled(LevelTranslator.toLevel(level));
    }

    @Override
    public String getName() {
        return logger.getName();
    }

    @Override
    public void setLevel(final Level newLevel) throws SecurityException {
        throw new UnsupportedOperationException("Cannot set level through log4j-api");
    }

    /**
     * Provides access to {@link Logger#setLevel(java.util.logging.Level)}. This method should only be used by child
     * classes.
     *
     * @see Logger#setLevel(java.util.logging.Level)
     */
    protected void doSetLevel(final Level newLevel) throws SecurityException {
        super.setLevel(newLevel);
    }

    /**
     * Unsupported operation.
     *
     * @throws UnsupportedOperationException always
     */
    @Override
    public void setParent(final Logger parent) {
        throw new UnsupportedOperationException("Cannot set parent logger");
    }

    @Override
    public void log(final Level level, final String msg) {
        if (getFilter() == null) {
            logger.log(LevelTranslator.toLevel(level), msg);
        } else {
            super.log(level, msg);
        }
    }

    @Override
    public void log(final Level level, final String msg, final Object param1) {
        if (getFilter() == null) {
            logger.log(LevelTranslator.toLevel(level), msg, param1);
        } else {
            super.log(level, msg, param1);
        }
    }

    @Override
    public void log(final Level level, final String msg, final Object[] params) {
        if (getFilter() == null) {
            logger.log(LevelTranslator.toLevel(level), msg, params);
        } else {
            super.log(level, msg, params);
        }
    }

    @Override
    public void log(final Level level, final String msg, final Throwable thrown) {
        if (getFilter() == null) {
            logger.log(LevelTranslator.toLevel(level), msg, thrown);
        } else {
            super.log(level, msg, thrown);
        }
    }

    @Override
    public void logp(final Level level, final String sourceClass, final String sourceMethod, final String msg) {
        log(level, msg);
    }

    @Override
    public void logp(final Level level, final String sourceClass, final String sourceMethod, final String msg,
                     final Object param1) {
        log(level, msg, param1);
    }

    @Override
    public void logp(final Level level, final String sourceClass, final String sourceMethod, final String msg,
                     final Object[] params) {
        log(level, msg, params);
    }

    @Override
    public void logp(final Level level, final String sourceClass, final String sourceMethod, final String msg,
                     final Throwable thrown) {
        log(level, msg, thrown);
    }

    @Override
    public void logrb(final Level level, final String sourceClass, final String sourceMethod, final String bundleName,
                      final String msg) {
        log(level, msg);
    }

    @Override
    public void logrb(final Level level, final String sourceClass, final String sourceMethod, final String bundleName,
                      final String msg, final Object param1) {
        log(level, msg, param1);
    }

    @Override
    public void logrb(final Level level, final String sourceClass, final String sourceMethod, final String bundleName,
                      final String msg, final Object[] params) {
        log(level, msg, params);
    }

    @Override
    public void logrb(final Level level, final String sourceClass, final String sourceMethod, final String bundleName,
                      final String msg, final Throwable thrown) {
        log(level, msg, thrown);
    }

    @Override
    public void entering(final String sourceClass, final String sourceMethod) {
        logger.entry();
    }

    @Override
    public void entering(final String sourceClass, final String sourceMethod, final Object param1) {
        logger.entry(param1);
    }

    @Override
    public void entering(final String sourceClass, final String sourceMethod, final Object[] params) {
        logger.entry(params);
    }

    @Override
    public void exiting(final String sourceClass, final String sourceMethod) {
        logger.exit();
    }

    @Override
    public void exiting(final String sourceClass, final String sourceMethod, final Object result) {
        logger.exit(result);
    }

    @Override
    public void throwing(final String sourceClass, final String sourceMethod, final Throwable thrown) {
        logger.throwing(thrown);
    }

    @Override
    public void severe(final String msg) {
        if (getFilter() == null) {
            logger.logIfEnabled(FQCN, org.apache.logging.log4j.Level.ERROR, null, msg);
        } else {
            super.severe(msg);
        }
    }

    @Override
    public void warning(final String msg) {
        if (getFilter() == null) {
            logger.logIfEnabled(FQCN, org.apache.logging.log4j.Level.WARN, null, msg);
        } else {
            super.warning(msg);
        }
    }

    @Override
    public void info(final String msg) {
        if (getFilter() == null) {
            logger.logIfEnabled(FQCN, org.apache.logging.log4j.Level.INFO, null, msg);
        } else {
            super.info(msg);
        }
    }

    @Override
    public void config(final String msg) {
        if (getFilter() == null) {
            logger.logIfEnabled(FQCN, LevelTranslator.CONFIG, null, msg);
        } else {
            super.config(msg);
        }
    }

    @Override
    public void fine(final String msg) {
        if (getFilter() == null) {
            logger.logIfEnabled(FQCN, org.apache.logging.log4j.Level.DEBUG, null, msg);
        } else {
            super.fine(msg);
        }
    }

    @Override
    public void finer(final String msg) {
        if (getFilter() == null) {
            logger.logIfEnabled(FQCN, org.apache.logging.log4j.Level.TRACE, null, msg);
        } else {
            super.finer(msg);
        }
    }

    @Override
    public void finest(final String msg) {
        if (getFilter() == null) {
            logger.logIfEnabled(FQCN, LevelTranslator.FINEST, null, msg);
        } else {
            super.finest(msg);
        }
    }
}

⏎ org/apache/logging/log4j/jul/ApiLogger.java

Or download all of them as a single archive file:

File name: log4j-jul-2.14.1-sources.jar
File size: 24567 bytes
Release date: 2021-03-06
Download 

⇒ Source Code for Apache Log4j Commons Logging Bridge

⇐ Source Code for Apache Log4j Core Implementation

⇑ Downloading and Reviewing Apache Log4j Packages

⇑⇑ FAQ for Apache Log4j