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Copyright (c) 2004-2011 QOS.ch All rights reserved. Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 package org.slf4j;
 
 import java.util.Map;
 
This class hides and serves as a substitute for the underlying logging system's MDC implementation.

If the underlying logging system offers MDC functionality, then SLF4J's MDC, i.e. this class, will delegate to the underlying system's MDC. Note that at this time, only two logging systems, namely log4j and logback, offer MDC functionality. For java.util.logging which does not support MDC, org.slf4j.helpers.BasicMDCAdapter will be used. For other systems, i.e slf4j-simple and slf4j-nop, org.slf4j.helpers.NOPMDCAdapter will be used.

Thus, as a SLF4J user, you can take advantage of MDC in the presence of log4j, logback, or java.util.logging, but without forcing these systems as dependencies upon your users.

For more information on MDC please see the chapter on MDC in the logback manual.

Please note that all methods in this class are static.

Author(s):
Ceki Gülcü
Since:
1.4.1
 
 public class MDC {
 
   static final String NULL_MDCA_URL = "http://www.slf4j.org/codes.html#null_MDCA";
   static final String NO_STATIC_MDC_BINDER_URL = "http://www.slf4j.org/codes.html#no_static_mdc_binder";
   static MDCAdapter mdcAdapter;
 
   private MDC() {
   }
 
   static {
     try {
     } catch (NoClassDefFoundError ncde) {
        = new NOPMDCAdapter();
       String msg = ncde.getMessage();
       if (msg != null && msg.indexOf("StaticMDCBinder") != -1) {
         Util.report("Failed to load class \"org.slf4j.impl.StaticMDCBinder\".");
         Util.report("Defaulting to no-operation MDCAdapter implementation.");
         Util
             .report("See " +  + " for further details.");
       } else {
         throw ncde;
       }
     } catch (Exception e) {
       // we should never get here
       Util.report("MDC binding unsuccessful."e);
     }
   }

  
Put a diagnostic context value (the val parameter) as identified with the key parameter into the current thread's diagnostic context map. The key parameter cannot be null. The val parameter can be null only if the underlying implementation supports it.

This method delegates all work to the MDC of the underlying logging system.

Parameters:
key non-null key
val value to put in the map
Throws:
java.lang.IllegalArgumentException in case the "key" parameter is null
  public static void put(String keyString val)
      throws IllegalArgumentException {
    if (key == null) {
      throw new IllegalArgumentException("key parameter cannot be null");
    }
    if ( == null) {
      throw new IllegalStateException("MDCAdapter cannot be null. See also "
          + );
    }
    .put(keyval);
  }

  
Get the diagnostic context identified by the key parameter. The key parameter cannot be null.

This method delegates all work to the MDC of the underlying logging system.

Parameters:
key
Returns:
the string value identified by the key parameter.
Throws:
java.lang.IllegalArgumentException in case the "key" parameter is null
  public static String get(String keythrows IllegalArgumentException {
    if (key == null) {
      throw new IllegalArgumentException("key parameter cannot be null");
    }
    if ( == null) {
      throw new IllegalStateException("MDCAdapter cannot be null. See also "
          + );
    }
    return .get(key);
  }

  
Remove the diagnostic context identified by the key parameter using the underlying system's MDC implementation. The key parameter cannot be null. This method does nothing if there is no previous value associated with key.

Parameters:
key
Throws:
java.lang.IllegalArgumentException in case the "key" parameter is null
  public static void remove(String keythrows IllegalArgumentException {
    if (key == null) {
      throw new IllegalArgumentException("key parameter cannot be null");
    }
    if ( == null) {
      throw new IllegalStateException("MDCAdapter cannot be null. See also "
          + );
    }
    .remove(key);
  }

  
Clear all entries in the MDC of the underlying implementation.
  public static void clear() {
    if ( == null) {
      throw new IllegalStateException("MDCAdapter cannot be null. See also "
          + );
    }
    .clear();
  }

  
Return a copy of the current thread's context map, with keys and values of type String. Returned value may be null.

Returns:
A copy of the current thread's context map. May be null.
Since:
1.5.1
  public static Map getCopyOfContextMap() {
    if ( == null) {
      throw new IllegalStateException("MDCAdapter cannot be null. See also "
          + );
    }
  }

  
Set the current thread's context map by first clearing any existing map and then copying the map passed as parameter. The context map passed as parameter must only contain keys and values of type String.

Parameters:
contextMap must contain only keys and values of type String
Since:
1.5.1
  public static void setContextMap(Map contextMap) {
    if ( == null) {
      throw new IllegalStateException("MDCAdapter cannot be null. See also "
          + );
    }
    .setContextMap(contextMap);
  }

  
Returns the MDCAdapter instance currently in use.

Returns:
the MDcAdapter instance currently in use.
Since:
1.4.2
  public static MDCAdapter getMDCAdapter() {
    return ;
  }
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