I assume the file is on the server where the applet resides, and not on the client machine?
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Apache POI library can read Excel files. You would create an HSSFWorkbook object from the file input stream, and then use the getSheet method to obtain a reference to the sheet you want to display. The sheet's getRow method gives you a reference to a row of cells, from which you can call getCell to get the contents of any particular cell.