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/Level.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.
 */

// Contributors:  Kitching Simon <Simon.Kitching@orange.ch>
//                Nicholas Wolff

package org.apache.log4j;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectStreamException;
import java.io.Serializable;

/**
   Defines the minimum set of levels recognized by the system, that is
   <code>OFF</code>, <code>FATAL</code>, <code>ERROR</code>,
   <code>WARN</code>, <code>INFO</code, <code>DEBUG</code> and
   <code>ALL</code>.

   <p>The <code>Level</code> class may be subclassed to define a larger
   level set.

   @author Ceki G&uuml;lc&uuml;

 */
public class Level extends Priority implements Serializable {

   /**
    * TRACE level integer value.
    * @since 1.2.12
    */
  public static final int TRACE_INT = 5000;

  /**
     The <code>OFF</code> has the highest possible rank and is
     intended to turn off logging.  */
  final static public Level OFF = new Level(OFF_INT, "OFF", 0);

  /**
     The <code>FATAL</code> level designates very severe error
     events that will presumably lead the application to abort.
   */
  final static public Level FATAL = new Level(FATAL_INT, "FATAL", 0);

  /**
     The <code>ERROR</code> level designates error events that
     might still allow the application to continue running.  */
  final static public Level ERROR = new Level(ERROR_INT, "ERROR", 3);

  /**
     The <code>WARN</code> level designates potentially harmful situations.
  */
  final static public Level WARN  = new Level(WARN_INT, "WARN",  4);

  /**
     The <code>INFO</code> level designates informational messages
     that highlight the progress of the application at coarse-grained
     level.  */
  final static public Level INFO  = new Level(INFO_INT, "INFO",  6);

  /**
     The <code>DEBUG</code> Level designates fine-grained
     informational events that are most useful to debug an
     application.  */
  final static public Level DEBUG = new Level(DEBUG_INT, "DEBUG", 7);

  /**
    * The <code>TRACE</code> Level designates finer-grained
    * informational events than the <code>DEBUG</code level.
   *  @since 1.2.12
    */
  public static final Level TRACE = new Level(TRACE_INT, "TRACE", 7);


  /**
     The <code>ALL</code> has the lowest possible rank and is intended to
     turn on all logging.  */
  final static public Level ALL = new Level(ALL_INT, "ALL", 7);

  /**
   * Serialization version id.
   */
  static final long serialVersionUID = 3491141966387921974L;

  /**
     Instantiate a Level object.
   */
  protected
  Level(int level, String levelStr, int syslogEquivalent) {
    super(level, levelStr, syslogEquivalent);
  }


  /**
     Convert the string passed as argument to a level. If the
     conversion fails, then this method returns {@link #DEBUG}. 
  */
  public
  static
  Level toLevel(String sArg) {
    return (Level) toLevel(sArg, Level.DEBUG);
  }

  /**
    Convert an integer passed as argument to a level. If the
    conversion fails, then this method returns {@link #DEBUG}.

  */
  public
  static
  Level toLevel(int val) {
    return (Level) toLevel(val, Level.DEBUG);
  }

  /**
    Convert an integer passed as argument to a level. If the
    conversion fails, then this method returns the specified default.
  */
  public
  static
  Level toLevel(int val, Level defaultLevel) {
    switch(val) {
    case ALL_INT: return ALL;
    case DEBUG_INT: return Level.DEBUG;
    case INFO_INT: return Level.INFO;
    case WARN_INT: return Level.WARN;
    case ERROR_INT: return Level.ERROR;
    case FATAL_INT: return Level.FATAL;
    case OFF_INT: return OFF;
    case TRACE_INT: return Level.TRACE;
    default: return defaultLevel;
    }
  }

  /**
     Convert the string passed as argument to a level. If the
     conversion fails, then this method returns the value of
     <code>defaultLevel</code>.  
  */
  public
  static
  Level toLevel(String sArg, Level defaultLevel) {                  
    if(sArg == null)
       return defaultLevel;
    
    String s = sArg.toUpperCase();

    if(s.equals("ALL")) return Level.ALL; 
    if(s.equals("DEBUG")) return Level.DEBUG; 
    if(s.equals("INFO"))  return Level.INFO;
    if(s.equals("WARN"))  return Level.WARN;  
    if(s.equals("ERROR")) return Level.ERROR;
    if(s.equals("FATAL")) return Level.FATAL;
    if(s.equals("OFF")) return Level.OFF;
    if(s.equals("TRACE")) return Level.TRACE;
    //
    //   For Turkish i problem, see bug 40937
    //
    if(s.equals("\u0130NFO")) return Level.INFO;
    return defaultLevel;
  }

    /**
     * Custom deserialization of Level.
     * @param s serialization stream.
     * @throws IOException if IO exception.
     * @throws ClassNotFoundException if class not found.
     */
    private void readObject(final ObjectInputStream s) throws IOException, ClassNotFoundException {
      s.defaultReadObject();
      level = s.readInt();
      syslogEquivalent = s.readInt();
      levelStr = s.readUTF();
      if (levelStr == null) {
          levelStr = "";
      }
    }

    /**
     * Serialize level.
     * @param s serialization stream.
     * @throws IOException if exception during serialization.
     */
    private void writeObject(final ObjectOutputStream s) throws IOException {
        s.defaultWriteObject();
        s.writeInt(level);
        s.writeInt(syslogEquivalent);
        s.writeUTF(levelStr);
    }

    /**
     * Resolved deserialized level to one of the stock instances.
     * May be overriden in classes derived from Level.
     * @return resolved object.
     * @throws ObjectStreamException if exception during resolution.
     */
    private Object readResolve() throws ObjectStreamException {
        //
        //  if the deserizalized object is exactly an instance of Level
        //
        if (getClass() == Level.class) {
            return toLevel(level);
        }
        //
        //   extension of Level can't substitute stock item
        //
        return this;
    }

}

⏎ org/apache/log4j/Level.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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