You need to apply a style to the cell. The style can include a number format.
DataFormat format = workbook.createDataFormat();
short fmt = format.getFormat("#0.0");
CellStyle style = workbook.createCellStyle();
style.setDataFormat(fmt);
…
cell.setCellStyle(style);
From: Syed Mudassir Ahmed [mai
https://github.com/apache/poi/blob/trunk/src/examples/src/org/apache/poi/xssf/eventusermodel/examples/FromHowTo.java
https://github.com/apache/poi/blob/trunk/src/examples/src/org/apache/poi/xssf/eventusermodel/XLSX2CSV.java
These are our 2 main streaming xlsx reading examples and both use SAXHelp
