Invalid header signature; IOException with Apache POI on excel document

In my case, the file was a CSV file saved with the .xls extension. Excel was able to open it without a problem, but POI was not.

If I find a better/more general solution, I'll come back and write it up here.

because you saved your file by Excel 2013. save As your file as excel 97-2003 format.

Try save it as csv file directly and use opencsv for your operations.
Use the following link to know about opencsv.
http://opencsv.sourceforge.net/#what-is-opencsv

Excel can open a csv, xls or even html table saved as xls.

So you can save the file as file_name.csv and can use opencsv for reading the file in your code.

Or else you can the file once in excel by save As excel 97-2003 workbook.

And then, POI itself can read the file :-)

If you flip the signature number round, you'll see the bytes of the start of your file:

0x000201060000FFFE -> 0xFE 0xFF 0x00 0x00 0x06 0x01 0x02 00

The first two bytes look like a Unicode BOM, 0xFEFF means 16 bit little endian. You then have some low control bytes, the hex codes for 0 then 258 then 2, so maybe it isn't a text file after all.

That file really isn't an OLE2 file, and POI is right to give you the error. I don't know what it is, but I'm guessing that perhaps it might be part of an OLE2 file without it's outer OLE2 wrapper? If you can open it with office, do a save-as and POI should be fine to open that. As it stands, that header isn't an OLE2 file header so POI can't open it for you.