title: Open EXISTING xls in Apache POI
body: <p>I have an existing file (C:\wb.xls) that I want to open and make changes to.  How in Apachie POI do you open an existing file?  All the documentation that I find has to go with creating a new file.  And if you know, how do you insert a new row at the top of the xls file or how to autoformat column widths?</p>