FileDocCategorySizeDatePackage
MDC.javaAPI DocApache log4j 1.2.154068Sat Aug 25 00:09:42 BST 2007org.apache.log4j

MDC

public class MDC extends Object
The MDC class is similar to the {@link NDC} class except that it is based on a map instead of a stack. It provides mapped diagnostic contexts. A Mapped Diagnostic Context, or MDC in short, is an instrument for distinguishing interleaved log output from different sources. Log output is typically interleaved when a server handles multiple clients near-simultaneously.

The MDC is managed on a per thread basis. A child thread automatically inherits a copy of the mapped diagnostic context of its parent.

The MDC class requires JDK 1.2 or above. Under JDK 1.1 the MDC will always return empty values but otherwise will not affect or harm your application.

since
1.2
author
Ceki Gülcü

Fields Summary
static final MDC
mdc
static final int
HT_SIZE
boolean
java1
Object
tlm
Constructors Summary
private MDC()

  
  
   
    java1 = Loader.isJava1();
    if(!java1) {
      tlm = new ThreadLocalMap();
    }
Methods Summary
public static java.lang.Objectget(java.lang.String key)
Get the context identified by the key parameter.

This method has no side effects.

    if (mdc != null) {
        return mdc.get0(key);
    }
    return null;
private java.lang.Objectget0(java.lang.String key)

    if(java1 || tlm == null) {
      return null;
    } else {       
      Hashtable ht = (Hashtable) ((ThreadLocalMap)tlm).get();
      if(ht != null && key != null) {
        return ht.get(key);
      } else {
        return null;
      }
    }
public static java.util.HashtablegetContext()
Get the current thread's MDC as a hashtable. This method is intended to be used internally.

    if (mdc != null) {
        return mdc.getContext0();
    } else {
        return null;
    }
private java.util.HashtablegetContext0()

     if(java1 || tlm == null) {
      return null;
    } else {       
      return (Hashtable) ((ThreadLocalMap)tlm).get();
    }
public static voidput(java.lang.String key, java.lang.Object o)
Put a context value (the o parameter) as identified with the key parameter into the current thread's context map.

If the current thread does not have a context map it is created as a side effect.

     if (mdc != null) {
         mdc.put0(key, o);
     }
private voidput0(java.lang.String key, java.lang.Object o)

    if(java1 || tlm == null) {
      return;
    } else {
      Hashtable ht = (Hashtable) ((ThreadLocalMap)tlm).get();
      if(ht == null) {
        ht = new Hashtable(HT_SIZE);
        ((ThreadLocalMap)tlm).set(ht);
      }    
      ht.put(key, o);
    }
public static voidremove(java.lang.String key)
Remove the the context identified by the key parameter.

    if (mdc != null) {
        mdc.remove0(key);
    }
private voidremove0(java.lang.String key)

    if(!java1 && tlm != null) {
      Hashtable ht = (Hashtable) ((ThreadLocalMap)tlm).get();
      if(ht != null) {
        ht.remove(key);
      } 
    }