org.slf4j

Class MDC

java.lang.Object

org.slf4j.MDC

public class MDC
extends Object

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, BasicMDCAdapter will be used. For other systems, i.e slf4j-simple and slf4j-nop, 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.

Since:

1.4.1

Author:

Ceki Gülcü

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	MDC.MDCCloseable An adapter to remove the key when done.

Method Summary

Methods

Modifier and Type	Method and Description
static void	clear() Clear all entries in the MDC of the underlying implementation.
static String	get(String key) Get the diagnostic context identified by the key parameter.
static Map<String,String>	getCopyOfContextMap() Return a copy of the current thread's context map, with keys and values of type String.
static MDCAdapter	getMDCAdapter() Returns the MDCAdapter instance currently in use.
static void	put(String key, String val) Put a diagnostic context value (the val parameter) as identified with the key parameter into the current thread's diagnostic context map.
static MDC.MDCCloseable	putCloseable(String key, String val) Put a diagnostic context value (the val parameter) as identified with the key parameter into the current thread's diagnostic context map.
static void	remove(String key) Remove the diagnostic context identified by the key parameter using the underlying system's MDC implementation.
static void	setContextMap(Map<String,String> contextMap) Set the current thread's context map by first clearing any existing map and then copying the map passed as parameter.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

put

public static void put(String key,
       String val)
                throws IllegalArgumentException

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:

IllegalArgumentException - in case the "key" parameter is null

putCloseable

public static MDC.MDCCloseable putCloseable(String key,
                            String val)
                                     throws IllegalArgumentException

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.

This method return a Closeable object who can remove key when close is called.

Useful with Java 7 for example : try(MDC.MDCCloseable closeable = MDC.putCloseable(key, value)) { .... }

Parameters:

key - non-null key

val - value to put in the map

Returns:

a Closeable who can remove key when close is called.

Throws:

IllegalArgumentException - in case the "key" parameter is null

get

public static String get(String key)
                  throws IllegalArgumentException

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:

IllegalArgumentException - in case the "key" parameter is null

remove

public static void remove(String key)
                   throws IllegalArgumentException

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:

IllegalArgumentException - in case the "key" parameter is null

clear

public static void clear()

Clear all entries in the MDC of the underlying implementation.

getCopyOfContextMap

public static Map<String,String> getCopyOfContextMap()

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

setContextMap

public static void setContextMap(Map<String,String> contextMap)

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

getMDCAdapter

public static MDCAdapter getMDCAdapter()

Returns the MDCAdapter instance currently in use.

Returns:

the MDcAdapter instance currently in use.

Since:

1.4.2