XSSFWorkbook is at: poi-ooxml-3.9-20121203.jar.org.apache.poi.xssf.usermodel.XSSFWorkbook.

HSSFWorkbook is at: poi-3.9-20121203.jar.org.apache.poi.hssf.usermodel.HSSFWorkbook.

Extended information:

The difference between XSSFWorkbook and HSSFWorkbook in the poi package in Apache:

HSSFWorkbook: It operates on versions before Excel 2003 (including 2003). The extension is .xls.

XSSFWorkbook: It is a version that operates Excel2007, and the extension is .xlsx.

For different versions of EXCEL documents, different tool classes must be used. If used incorrectly, the following error message will be prompted.

org.apache.poi.openxml4j.exceptions.InvalidOperationException.

org.apache.poi.poifs.filesystem.OfficeXmlFileException.

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Security: JAR file contents can be digitally signed. This way, a tool that recognizes the signature can selectively grant you software security privileges that no other file can, and it can also detect whether the code has been tampered with.

Reduce download time: If an applet is bundled into a JAR file, the browser can download the applet's class files and related resources in one HTTP? transaction, rather than opening each file A new connection.

Compression: The JAR format allows you to compress files for greater storage efficiency.