If you deal with web applications you probably have already dealt with export data to Excel. There are several options to prepare data for Excel:

• generate CSV;
• generate HTML that excel understands;
• generate XML in Spreadsheet 2003 format;
• generate data using Open XML SDK or some other 3rd party libraries;
• generate data in XLSX format, according to Open XML specification.

You may find a good article with pros and cons of each solution here. We, in our turn, would like to share our experience in this field. Let's start from requirements:

• Often we have to export huge data-sets.
• We should be able to format, parametrize and to apply different styles to the exported data.
• There are cases when exported data may contain more than one table per sheet or even more than one sheet.
• Some exported data have to be illustrated with charts.

All these requirements led us to a solution based on XSLT processing of streamed data. The advantage of this solution is that the result is immediately forwarded to a client as fast as XSLT starts to generate output. Such approach is much productive than generating of XLSX using of Open XML SDK or any other third party library, since it avoids keeping a huge data-sets in memory on the server side.

Another advantage - is simple maintenance, as we achieve clear separation of data and presentation layers. On each request to change formatting or apply another style to a cell you just have to modify xslt file(s) that generate variable parts of XLSX.

As result, our clients get XLSX files according with Open XML specifications. The details of implementations of our solution see in our next posts.