Module org.slf4j
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.
      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