public static String objectId(Object o) {
        if (o == null) {
            return "null";
        } else {
            return o.getClass().getName() + "@" + System.identityHashCode(o);
        }
    }
Returns a string that uniquely identifies the specified object, including
its class.
<p>
The returned string is of form "classname@hashcode", i.e. is the same as the
return value of the Object.toString() method, but works even when the
specified object's class has overridden the toString method.

@param o
               may be null.
@return a string of form classname@hashcode, or "null" if param o is null.
@since 1.1
jcl-over-slf4j/src/main/java/org/apache/commons/logging/LogFactory.java