Apache POI

Apache POI is a set of Java APIs that can transfer data to and from Excel and other Microsoft Office file formats. It can be used for extracting text, loading tabular data and generate a document index.
The users who need to export data from Java applications usually have to deal with plain text, CSV or XML files. In order to use these files in other applications, the users need to use additional conversion tools or format the data manually.
A developer can use the components from this package in order to improve the user experience by exporting tabular data to Excel documents. Additional components for Word, Access and other programs are also included.
The APIs are able to convert the data to a format that complies with the Office OpenXML standard which allows you to generate XLSX, DOCX or PPTX files. These formats are supported by the latest versions of Microsoft Office and by other applications such as OpenOffice or LibreOffice.
Addtional Java libraries are available if you need to work with other Office files such as the Outlook messages or the Visio documents. However, each component is developed separately which means that the performance is different.
Some of the libraries support AES or RC4 encryption which allows the applications to read data from password protected files. Unfortunately, the support is not available for all file types.
If you need to create Java apps that can load data from Excel documents or PowerPoint presentations, Apache POI is good tool.