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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.
 */

package org.apache.log4j.helpers;

/**
   This class used to output log statements from within the log4j package.

   Log4j components cannot make log4j logging calls. However, it is
   sometimes useful for the user to learn about what log4j is
   doing. You can enable log4j internal logging by defining the
   log4j.configDebug variable.

   
All log4j internal debug calls go to System.out
   where as internal error messages are sent to
   System.err. All internal messages are prepended with
   the string "log4j: ".

   @since 0.8.2
   @author Ceki Gülcü
*/
public class LogLog {

    /**
       Defining this value makes log4j print log4j-internal debug
       statements to System.out.
    
      
 The value of this string is log4j.debug.
    
      
Note that the search for all option names is case sensitive.  */
    public static final String DEBUG_KEY = "log4j.debug";

    /**
       Defining this value makes log4j components print log4j-internal
       debug statements to System.out.
    
      
 The value of this string is log4j.configDebug.
    
      Note that the search for all option names is case sensitive.
    
      @deprecated Use {@link #DEBUG_KEY} instead.
    */
    public static final String CONFIG_DEBUG_KEY = "log4j.configDebug";

    protected static boolean debugEnabled = false;

    /**
       In quietMode not even errors generate any output.
     */
    private static boolean quietMode = false;

    private static final String PREFIX = "log4j: ";
    private static final String ERR_PREFIX = "log4j:ERROR ";
    private static final String WARN_PREFIX = "log4j:WARN ";

    static {
    }

    /**
       Allows to enable/disable log4j internal logging.
     */
    static public void setInternalDebugging(boolean enabled) {
        debugEnabled = enabled;
    }

    /**
       This method is used to output log4j internal debug
       statements. Output goes to System.out.
    */
    public static void debug(String msg) {
        if (debugEnabled && !quietMode) {
            System.out.println(PREFIX + msg);
        }
    }

    /**
       This method is used to output log4j internal debug
       statements. Output goes to System.out.
    */
    public static void debug(String msg, Throwable t) {
        if (debugEnabled && !quietMode) {
            System.out.println(PREFIX + msg);
            if (t != null)
                t.printStackTrace(System.out);
        }
    }

    /**
       This method is used to output log4j internal error
       statements. There is no way to disable error statements.
       Output goes to System.err.
    */
    public static void error(String msg) {
        if (quietMode)
            return;
        System.err.println(ERR_PREFIX + msg);
    }

    /**
       This method is used to output log4j internal error
       statements. There is no way to disable error statements.
       Output goes to System.err.
    */
    public static void error(String msg, Throwable t) {
        if (quietMode)
            return;

        System.err.println(ERR_PREFIX + msg);
        if (t != null) {
            t.printStackTrace();
        }
    }

    /**
       In quite mode no LogLog generates strictly no output, not even
       for errors.
    
       @param quietMode A true for not
    */
    public static void setQuietMode(boolean quietMode) {
        LogLog.quietMode = quietMode;
    }

    /**
       This method is used to output log4j internal warning
       statements. There is no way to disable warning statements.
       Output goes to System.err.  */
    public static void warn(String msg) {
        if (quietMode)
            return;

        System.err.println(WARN_PREFIX + msg);
    }

    /**
       This method is used to output log4j internal warnings. There is
       no way to disable warning statements.  Output goes to
       System.err.  */
    public static void warn(String msg, Throwable t) {
        if (quietMode)
            return;

        System.err.println(WARN_PREFIX + msg);
        if (t != null) {
            t.printStackTrace();
        }
    }
}