Initiates server side document loading. Please note that prior to calling complete() all
Sources must have been added or appended to the Reader.
The client is notified via AsyncCallback about the read status. The
AsyncCallbacks onSuccess() method will be called after the first
DocumentReadResult has successfully been processed. Then a document will be available on
the client side and the client can start to load the document into the viewer. Usually this will
be done by calling viewer.getPageView().setDocument(result) (where "result" is the callback's
result object, a Document instance).
Subsequent pages will be loaded asynchronously - processing these will be handled by appropriate
listeners.
Parameters:
source -
callback - Called when the Document is available for the client.