Package org.slf4j

Class MDC

  • public class MDC
extends java.lang.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

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      static void clear()
      Clear all entries in the MDC of the underlying implementation.
      static java.lang.String get​(java.lang.String key)
      Get the diagnostic context identified by the key parameter.
      static java.util.Map<java.lang.String,​java.lang.String> getCopyOfContextMap()
      Return a copy of the current thread's context map, with keys and values of type String.
      java.util.Deque<java.lang.String> getCopyOfDequeByKey​(java.lang.String key)
      Returns a copy of the deque(stack) referenced by 'key'.
      static MDCAdapter getMDCAdapter()
      Returns the MDCAdapter instance currently in use.
      static java.lang.String popByKey​(java.lang.String key)
      Pop the stack referenced by 'key' and return the value possibly null.
      static void pushByKey​(java.lang.String key, java.lang.String value)
      Push a value into the deque(stack) referenced by 'key'.
      static void put​(java.lang.String key, java.lang.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​(java.lang.String key, java.lang.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​(java.lang.String key)
      Remove the diagnostic context identified by the key parameter using the underlying system's MDC implementation.
      static void setContextMap​(java.util.Map<java.lang.String,​java.lang.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​(java.lang.String key,
                       java.lang.String val)
                throws java.lang.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:
        java.lang.IllegalArgumentException - in case the "key" parameter is null

      • putCloseable

        public static MDC.MDCCloseable putCloseable​(java.lang.String key,
                                            java.lang.String val)
                                     throws java.lang.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:
        java.lang.IllegalArgumentException - in case the "key" parameter is null

      • get

        public static java.lang.String get​(java.lang.String key)
                            throws java.lang.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:
        java.lang.IllegalArgumentException - in case the "key" parameter is null

      • remove

        public static void remove​(java.lang.String key)
                   throws java.lang.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:
        java.lang.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 java.util.Map<java.lang.String,​java.lang.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​(java.util.Map<java.lang.String,​java.lang.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​(java.lang.String key,
                             java.lang.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 java.lang.String popByKey​(java.lang.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 java.util.Deque<java.lang.String> getCopyOfDequeByKey​(java.lang.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