protected void setDispatchHandler(DispatchHandler dispatchHandler) {
        this.dispatchHandler = dispatchHandler;
    }
Returns the last time a full Document was read or a heartbeat was received. Hearbeats
are represented as whitespaces or \n received while a Document is not being parsed.

@return the time in milliseconds when the last document or heartbeat was received.
xmppserver/src/main/java/org/dom4j/io/XMPPPacketReader.java