I need to add the apache poi to my project (I need hssf, ss and xssf). I downloaded a jar file from the internet but it does not contain xssf. I went to http://poi.apache.org/ a
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You should head to the Apache POI Download Page, and then download the binary release. The binary releases have -bin- in their file names. The binary releases contain the POI jars, and their dependencies.
What you've downloaded with -src- in the name is the source package, which contains everything you need to build Apache POI yourself, but if you just want to get started you're much better off with the pre-compiled binary package.