Parse SpreadsheetML using Java

You need to parse the Excel 2003 XML file

<Workbook xmlns="urn:schemas-microsoft-com:office:spreadsheet" 
  xmlns:o="urn:schemas-microsoft-com:office:office" 
  xmlns:x="urn:schemas-microsoft-com:office:excel" 
  xmlns:ss="urn:schemas-microsoft-com:office:spreadsheet" 
  xmlns:html="http://www.w3.org/TR/REC-html40">

      

        
        
        
      

    

The file is not zipped as xslt, it is one xml file. So when trying to parse it with Apache POI got an exception error in opening zip file

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What is the best way to parse such a SpreadsheetML file?