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/SLF4JLoggerContextFactory.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 java.net.URI;

import org.apache.logging.log4j.spi.LoggerContext;
import org.apache.logging.log4j.spi.LoggerContextFactory;
import org.apache.logging.log4j.status.StatusLogger;
import org.apache.logging.log4j.util.LoaderUtil;

/**
 *
 */
public class SLF4JLoggerContextFactory implements LoggerContextFactory {
    private static final StatusLogger LOGGER = StatusLogger.getLogger();
    private static LoggerContext context = new SLF4JLoggerContext();

    public SLF4JLoggerContextFactory() {
        // LOG4J2-230, LOG4J2-204 (improve error reporting when misconfigured)
        boolean misconfigured = false;
        try {
            LoaderUtil.loadClass("org.slf4j.helpers.Log4jLoggerFactory");
            misconfigured = true;
        } catch (final ClassNotFoundException classNotFoundIsGood) {
            LOGGER.debug("org.slf4j.helpers.Log4jLoggerFactory is not on classpath. Good!");
        }
        if (misconfigured) {
            throw new IllegalStateException("slf4j-impl jar is mutually exclusive with log4j-to-slf4j jar "
                    + "(the first routes calls from SLF4J to Log4j, the second from Log4j to SLF4J)");
        }
    }

    @Override
    public LoggerContext getContext(final String fqcn, final ClassLoader loader, final Object externalContext,
                                    final boolean currentContext) {
        return context;
    }

    @Override
    public LoggerContext getContext(final String fqcn, final ClassLoader loader, final Object externalContext,
                                    final boolean currentContext, final URI configLocation, final String name) {
        return context;
    }

    @Override
    public void removeContext(final LoggerContext ignored) {
    }
}

⏎ org/apache/logging/slf4j/SLF4JLoggerContextFactory.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