Apache Log4j to SLF4J Adapter allows applications coded to the Log4j 2 API to be routed to SLF4J. Use of this adapter may cause some loss of performance as the Log4j 2 Messages must be formatted before they can be passed to SLF4J.

Bytecode (Java 8) for Apache Log4j to SLF4J Adapter is provided in a separate JAR file like log4j-to-slf4j-2.14.1.jar.

Source Code files for Apache Log4j IOStreams 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 to SLF4J Adapter 2.14.1 below.

⏎ org/apache/logging/slf4j/SLF4JLogger.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.slf4j;

import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.Marker;
import org.apache.logging.log4j.message.LoggerNameAwareMessage;
import org.apache.logging.log4j.message.Message;
import org.apache.logging.log4j.message.MessageFactory;
import org.apache.logging.log4j.spi.AbstractLogger;
import org.slf4j.MarkerFactory;
import org.slf4j.spi.LocationAwareLogger;

/**
 *
 */
public class SLF4JLogger extends AbstractLogger {

    private static final long serialVersionUID = 1L;
    private final org.slf4j.Logger logger;
    private final LocationAwareLogger locationAwareLogger;

    public SLF4JLogger(final String name, final MessageFactory messageFactory, final org.slf4j.Logger logger) {
        super(name, messageFactory);
        this.logger = logger;
        this.locationAwareLogger = logger instanceof LocationAwareLogger ? (LocationAwareLogger) logger : null;
    }

    public SLF4JLogger(final String name, final org.slf4j.Logger logger) {
        super(name);
        this.logger = logger;
        this.locationAwareLogger = logger instanceof LocationAwareLogger ? (LocationAwareLogger) logger : null;
    }

    private int convertLevel(final Level level) {
        switch (level.getStandardLevel()) {
            case DEBUG :
                return LocationAwareLogger.DEBUG_INT;
            case TRACE :
                return LocationAwareLogger.TRACE_INT;
            case INFO :
                return LocationAwareLogger.INFO_INT;
            case WARN :
                return LocationAwareLogger.WARN_INT;
            case ERROR :
                return LocationAwareLogger.ERROR_INT;
            default :
                return LocationAwareLogger.ERROR_INT;
        }
    }

    @Override
    public Level getLevel() {
        if (logger.isTraceEnabled()) {
            return Level.TRACE;
        }
        if (logger.isDebugEnabled()) {
            return Level.DEBUG;
        }
        if (logger.isInfoEnabled()) {
            return Level.INFO;
        }
        if (logger.isWarnEnabled()) {
            return Level.WARN;
        }
        if (logger.isErrorEnabled()) {
            return Level.ERROR;
        }
        // Option: throw new IllegalStateException("Unknown SLF4JLevel");
        // Option: return Level.ALL;
        return Level.OFF;
    }

    public org.slf4j.Logger getLogger() {
        return locationAwareLogger != null ? locationAwareLogger : logger;
    }

    private org.slf4j.Marker getMarker(final Marker marker) {
        if (marker == null) {
            return null;
        }
        final org.slf4j.Marker slf4jMarker = MarkerFactory.getMarker(marker.getName());
        final Marker[] parents = marker.getParents();
        if (parents != null) {
            for (final Marker parent : parents) {
                final org.slf4j.Marker slf4jParent = getMarker(parent);
                if (!slf4jMarker.contains(slf4jParent)) {
                    slf4jMarker.add(slf4jParent);
                }
            }
        }
        return slf4jMarker;
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final Message data, final Throwable t) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final CharSequence data, final Throwable t) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final Object data, final Throwable t) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String data) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String data, final Object... p1) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String message, final Object p0) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String message, final Object p0,
            final Object p1) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String message, final Object p0,
            final Object p1, final Object p2) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String message, final Object p0,
            final Object p1, final Object p2, final Object p3) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String message, final Object p0,
            final Object p1, final Object p2, final Object p3,
            final Object p4) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String message, final Object p0,
            final Object p1, final Object p2, final Object p3,
            final Object p4, final Object p5) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String message, final Object p0,
            final Object p1, final Object p2, final Object p3,
            final Object p4, final Object p5, final Object p6) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String message, final Object p0,
            final Object p1, final Object p2, final Object p3,
            final Object p4, final Object p5, final Object p6,
            final Object p7) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String message, final Object p0,
            final Object p1, final Object p2, final Object p3,
            final Object p4, final Object p5, final Object p6,
            final Object p7, final Object p8) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String message, final Object p0,
            final Object p1, final Object p2, final Object p3,
            final Object p4, final Object p5, final Object p6,
            final Object p7, final Object p8, final Object p9) {
        return isEnabledFor(level, marker);
    }

    @Override
    public boolean isEnabled(final Level level, final Marker marker, final String data, final Throwable t) {
        return isEnabledFor(level, marker);
    }

    private boolean isEnabledFor(final Level level, final Marker marker) {
        final org.slf4j.Marker slf4jMarker = getMarker(marker);
        switch (level.getStandardLevel()) {
            case DEBUG :
                return logger.isDebugEnabled(slf4jMarker);
            case TRACE :
                return logger.isTraceEnabled(slf4jMarker);
            case INFO :
                return logger.isInfoEnabled(slf4jMarker);
            case WARN :
                return logger.isWarnEnabled(slf4jMarker);
            case ERROR :
                return logger.isErrorEnabled(slf4jMarker);
            default :
                return logger.isErrorEnabled(slf4jMarker);

        }
    }

    @Override
    public void logMessage(final String fqcn, final Level level, final Marker marker, final Message message, final Throwable t) {
        if (locationAwareLogger != null) {
            if (message instanceof LoggerNameAwareMessage) {
                ((LoggerNameAwareMessage) message).setLoggerName(getName());
            }
            locationAwareLogger.log(getMarker(marker), fqcn, convertLevel(level), message.getFormattedMessage(),
                    message.getParameters(), t);
        } else {
            switch (level.getStandardLevel()) {
                case DEBUG :
                    logger.debug(getMarker(marker), message.getFormattedMessage(), message.getParameters(), t);
                    break;
                case TRACE :
                    logger.trace(getMarker(marker), message.getFormattedMessage(), message.getParameters(), t);
                    break;
                case INFO :
                    logger.info(getMarker(marker), message.getFormattedMessage(), message.getParameters(), t);
                    break;
                case WARN :
                    logger.warn(getMarker(marker), message.getFormattedMessage(), message.getParameters(), t);
                    break;
                case ERROR :
                    logger.error(getMarker(marker), message.getFormattedMessage(), message.getParameters(), t);
                    break;
                default :
                    logger.error(getMarker(marker), message.getFormattedMessage(), message.getParameters(), t);
                    break;
            }
        }
    }

}

⏎ org/apache/logging/slf4j/SLF4JLogger.java

Or download all of them as a single archive file:

File name: log4j-to-slf4j-2.14.1-sources.jar
File size: 15755 bytes
Release date: 2021-03-06
Download 

⇒ Source Code for Apache Log4j IOStreams

⇐ Source Code for Apache Log4j SLF4J Binding

⇑ Downloading and Reviewing Apache Log4j Packages

⇑⇑ FAQ for Apache Log4j