code: public Object setSessionAttribute(final String _key,
                                        final Object _value)
      {
          return this.sessionAttributes.put(_key, _value);
      }
docs: Associates the specified value with the specified key in the session
  attributes. If the session attributes previously contained a mapping for
  this key, the old value is replaced by the specified value.
  
  @param _key key name of the attribute to set
  @param _value value of the attribute to set
  @return Object
  @see #sessionAttributes
  @see #containsSessionAttribute
  @see #getSessionAttribute