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Log4j implemented over SLF4J
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/*
 * Copyright 2001-2004 The Apache Software Foundation.
 *
 * Licensed 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 
//                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
   OFF, FATAL, ERROR,
   WARN, INFO, DEBUG and
   ALL.

   The Level class may be subclassed to define a larger
   level set.

   @author Ceki Gülcü

 */
public class Level extends Priority implements Serializable {

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

    // match jboss' xlevel
    public static final int X_TRACE_INT = DEBUG_INT - 100;

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

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

    /**
       The INFO 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 DEBUG 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 TRACE Level designates finer-grained
      * informational events than the DEBUGALL 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
       defaultLevel.  
    */
    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;
        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 overridden in classes derived from Level.
     * @return resolved object.
     * @throws ObjectStreamException if exception during resolution.
     */
    private Object readResolve() throws ObjectStreamException {
        //
        // if the deserialized object is exactly an instance of Level
        //
        if (getClass() == Level.class) {
            return toLevel(level);
        }
        //
        // extension of Level can't substitute stock item
        //
        return this;
    }
}