public static void put(String key, String val) throws IllegalArgumentException {
        if (key == null) {
            throw new IllegalArgumentException("key parameter cannot be null");
        }
        if (getMDCAdapter() == null) {
            throw new IllegalStateException(MDC_APAPTER_CANNOT_BE_NULL_MESSAGE);
        }
        getMDCAdapter().put(key, val);
    }
Put a diagnostic context value (the <code>val</code> parameter) as identified with the
<code>key</code> parameter into the current thread's diagnostic context map. The
<code>key</code> parameter cannot be null. The <code>val</code> parameter
can be null only if the underlying implementation supports it.

<p>
This method delegates all work to the MDC of the underlying logging system.

@param key non-null key 
@param val value to put in the map

@throws IllegalArgumentException
          in case the "key" parameter is null
slf4j-api/src/main/java/org/slf4j/MDC.java