Apache Log4j provides the interface that applications should code to and provides the adapter components required for implementers to create a logging implementation.

Bytecode (Java 1.4) for Apache Log4j is provided in a JAR file like log4j-1.2.17.jar.

Source Code files for Apache Log4j are provided in both binary packge like log4j-1.2.17.zip and source package like log4j-1.2.17-sources.zip. You can download them at Apache Log4j Website.

You can also browse Source Code files for Apache Log4j 1.2.17 below.

⏎ org/apache/log4j/LogManager.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.log4j;

import org.apache.log4j.spi.LoggerRepository;
import org.apache.log4j.spi.LoggerFactory;
import org.apache.log4j.spi.RepositorySelector;
import org.apache.log4j.spi.DefaultRepositorySelector;
import org.apache.log4j.spi.RootLogger;
import org.apache.log4j.spi.NOPLoggerRepository;
import org.apache.log4j.helpers.Loader;
import org.apache.log4j.helpers.OptionConverter;
import org.apache.log4j.helpers.LogLog;

import java.net.URL;
import java.net.MalformedURLException;


import java.util.Enumeration;
import java.io.StringWriter;
import java.io.PrintWriter;

/**
 * Use the <code>LogManager</code> class to retreive {@link Logger}
 * instances or to operate on the current {@link
 * LoggerRepository}. When the <code>LogManager</code> class is loaded
 * into memory the default initalzation procedure is inititated. The
 * default intialization procedure</a> is described in the <a
 * href="../../../../manual.html#defaultInit">short log4j manual</a>.
 *
 * @author Ceki G&uuml;lc&uuml; */
public class LogManager {

  /**
   * @deprecated This variable is for internal use only. It will
   * become package protected in future versions.
   * */
  static public final String DEFAULT_CONFIGURATION_FILE = "log4j.properties";
  
  static final String DEFAULT_XML_CONFIGURATION_FILE = "log4j.xml";  
   
  /**
   * @deprecated This variable is for internal use only. It will
   * become private in future versions.
   * */
  static final public String DEFAULT_CONFIGURATION_KEY="log4j.configuration";

  /**
   * @deprecated This variable is for internal use only. It will
   * become private in future versions.
   * */
  static final public String CONFIGURATOR_CLASS_KEY="log4j.configuratorClass";

  /**
  * @deprecated This variable is for internal use only. It will
  * become private in future versions.
  */
  public static final String DEFAULT_INIT_OVERRIDE_KEY = 
                                                 "log4j.defaultInitOverride";


  static private Object guard = null;
  static private RepositorySelector repositorySelector;

  static {
    // By default we use a DefaultRepositorySelector which always returns 'h'.
    Hierarchy h = new Hierarchy(new RootLogger((Level) Level.DEBUG));
    repositorySelector = new DefaultRepositorySelector(h);

    /** Search for the properties file log4j.properties in the CLASSPATH.  */
    String override =OptionConverter.getSystemProperty(DEFAULT_INIT_OVERRIDE_KEY,
						       null);

    // if there is no default init override, then get the resource
    // specified by the user or the default config file.
    if(override == null || "false".equalsIgnoreCase(override)) {

      String configurationOptionStr = OptionConverter.getSystemProperty(
							  DEFAULT_CONFIGURATION_KEY, 
							  null);

      String configuratorClassName = OptionConverter.getSystemProperty(
                                                   CONFIGURATOR_CLASS_KEY, 
						   null);

      URL url = null;

      // if the user has not specified the log4j.configuration
      // property, we search first for the file "log4j.xml" and then
      // "log4j.properties"
      if(configurationOptionStr == null) {	
	url = Loader.getResource(DEFAULT_XML_CONFIGURATION_FILE);
	if(url == null) {
	  url = Loader.getResource(DEFAULT_CONFIGURATION_FILE);
	}
      } else {
	try {
	  url = new URL(configurationOptionStr);
	} catch (MalformedURLException ex) {
	  // so, resource is not a URL:
	  // attempt to get the resource from the class path
	  url = Loader.getResource(configurationOptionStr); 
	}	
      }
      
      // If we have a non-null url, then delegate the rest of the
      // configuration to the OptionConverter.selectAndConfigure
      // method.
      if(url != null) {
	    LogLog.debug("Using URL ["+url+"] for automatic log4j configuration.");
        try {
            OptionConverter.selectAndConfigure(url, configuratorClassName,
					   LogManager.getLoggerRepository());
        } catch (NoClassDefFoundError e) {
            LogLog.warn("Error during default initialization", e);
        }
      } else {
	    LogLog.debug("Could not find resource: ["+configurationOptionStr+"].");
      }
    } else {
        LogLog.debug("Default initialization of overridden by " + 
            DEFAULT_INIT_OVERRIDE_KEY + "property."); 
    }  
  } 

  /**
     Sets <code>LoggerFactory</code> but only if the correct
     <em>guard</em> is passed as parameter.
     
     <p>Initally the guard is null.  If the guard is
     <code>null</code>, then invoking this method sets the logger
     factory and the guard. Following invocations will throw a {@link
     IllegalArgumentException}, unless the previously set
     <code>guard</code> is passed as the second parameter.

     <p>This allows a high-level component to set the {@link
     RepositorySelector} used by the <code>LogManager</code>.
     
     <p>For example, when tomcat starts it will be able to install its
     own repository selector. However, if and when Tomcat is embedded
     within JBoss, then JBoss will install its own repository selector
     and Tomcat will use the repository selector set by its container,
     JBoss.  */
  static
  public
  void setRepositorySelector(RepositorySelector selector, Object guard) 
                                                 throws IllegalArgumentException {
    if((LogManager.guard != null) && (LogManager.guard != guard)) {
      throw new IllegalArgumentException(
           "Attempted to reset the LoggerFactory without possessing the guard.");
    }

    if(selector == null) {
      throw new IllegalArgumentException("RepositorySelector must be non-null.");
    }

    LogManager.guard = guard;
    LogManager.repositorySelector = selector;
  }


    /**
     * This method tests if called from a method that
     * is known to result in class members being abnormally
     * set to null but is assumed to be harmless since the
     * all classes are in the process of being unloaded.
     *
     * @param ex exception used to determine calling stack.
     * @return true if calling stack is recognized as likely safe.
     */
  private static boolean isLikelySafeScenario(final Exception ex) {
      StringWriter stringWriter = new StringWriter();
      ex.printStackTrace(new PrintWriter(stringWriter));
      String msg = stringWriter.toString();
      return msg.indexOf("org.apache.catalina.loader.WebappClassLoader.stop") != -1;
  }

  static
  public
  LoggerRepository getLoggerRepository() {
    if (repositorySelector == null) {
        repositorySelector = new DefaultRepositorySelector(new NOPLoggerRepository());
        guard = null;
        Exception ex = new IllegalStateException("Class invariant violation");
        String msg =
                "log4j called after unloading, see http://logging.apache.org/log4j/1.2/faq.html#unload.";
        if (isLikelySafeScenario(ex)) {
            LogLog.debug(msg, ex);
        } else {
            LogLog.error(msg, ex);
        }
    }
    return repositorySelector.getLoggerRepository();
  }

  /**
     Retrieve the appropriate root logger.
   */
  public
  static 
  Logger getRootLogger() {
     // Delegate the actual manufacturing of the logger to the logger repository.
    return getLoggerRepository().getRootLogger();
  }

  /**
     Retrieve the appropriate {@link Logger} instance.  
  */
  public
  static 
  Logger getLogger(final String name) {
     // Delegate the actual manufacturing of the logger to the logger repository.
    return getLoggerRepository().getLogger(name);
  }

 /**
     Retrieve the appropriate {@link Logger} instance.  
  */
  public
  static 
  Logger getLogger(final Class clazz) {
     // Delegate the actual manufacturing of the logger to the logger repository.
    return getLoggerRepository().getLogger(clazz.getName());
  }


  /**
     Retrieve the appropriate {@link Logger} instance.  
  */
  public
  static 
  Logger getLogger(final String name, final LoggerFactory factory) {
     // Delegate the actual manufacturing of the logger to the logger repository.
    return getLoggerRepository().getLogger(name, factory);
  }  

  public
  static
  Logger exists(final String name) {
    return getLoggerRepository().exists(name);
  }

  public
  static
  Enumeration getCurrentLoggers() {
    return getLoggerRepository().getCurrentLoggers();
  }

  public
  static
  void shutdown() {
    getLoggerRepository().shutdown();
  }

  public
  static
  void resetConfiguration() {
    getLoggerRepository().resetConfiguration();
  }
}

⏎ org/apache/log4j/LogManager.java

Or download all of them as a single archive file:

File name: log4j-1.2.17-sources.jar
File size: 481200 bytes
Release date: 2012-05-06
Download 

⇒ Download and Install apache-log4j-1.2.15.zip

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