Package 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	Description
static class	MDC.MDCCloseable	An adapter to remove the key when done.

Method Summary

Modifier and Type	Method	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.
Deque<String>	getCopyOfDequeByKey(String key)	Returns a copy of the deque(stack) referenced by 'key'.
static MDCAdapter	getMDCAdapter()	Returns the MDCAdapter instance currently in use.
static String	popByKey(String key)	Pop the stack referenced by 'key' and return the value possibly null.
static void	pushByKey(String key, String value)	Push a value into the deque(stack) referenced by 'key'.
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 Details

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 - a 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 - a 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. Null valued argument is allowed (since SLF4J version 2.0.0).

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. Since 2.0.17, if the MDCAdapter instance is null, then this method set it to use the adapter returned by the SLF4JProvider. However, in the vast majority of cases the MDCAdapter will be set earlier (during initialization) by LoggerFactory.

Returns:

the MDcAdapter instance currently in use.

Since:

1.4.2

pushByKey

public static void pushByKey(String key,
 String value)

Push a value into the deque(stack) referenced by 'key'.

Parameters:

key - identifies the appropriate stack

value - the value to push into the stack

Since:

2.0.0

popByKey

public static String popByKey(String key)

Pop the stack referenced by 'key' and return the value possibly null.

Parameters:

key - identifies the deque(stack)

Returns:

the value just popped. May be null/

Since:

2.0.0

getCopyOfDequeByKey

public Deque<String> getCopyOfDequeByKey(String key)

Returns a copy of the deque(stack) referenced by 'key'. May be null.

Parameters:

key - identifies the stack

Returns:

copy of stack referenced by 'key'. May be null.

Since:

2.0.0