Can you please provide the link for the Aspose.cells.viewer dll file
Aspose.Cells.Viewer is an open source app, you may get its source project here.
for Aspose online excel viewer / editor
it basicly use GridJs .
you can use GridJs or GridWeb to develop such web applications .
you can find the example here
we will have also scheduled GridJs java version in the next plan,it will be available in java soon