API to write huge excel files using java

Question

I am looking to write to an excel (.xls MS Excel 2003 format) file programatically using Java. The excel output files may contain ~200,000 rows which I plan to split over n

Answer 1

All existing Java APIs try to build the whole document in RAM at once. Try to write an XML file which conforms to the new xslx file format instead. To get you started, I suggest to build a small file in the desired form in Excel and save it. Then open it and examine the structure and replace the parts you want.

Wikipedia has a good article about the overall format.

Answer 2

Consider using CSV format. This way you aren't limited by memory anymore --well, maybe only during prepopulating the data for CSV, but this can be done efficiently as well, for example querying subsets of rows from DB using for example LIMIT/OFFSET and immediately write it to file instead of hauling the entire DB table contents into Java's memory before writing any line. The Excel limitation of the amount rows in one "sheet" will increase to about one million.

That said, if the data is actually coming from a DB, then I would highly reconsider if Java is the right tool for this. Most decent DB's have an export-to-CSV function which can do this task undoubtely much more efficient. In case of for example MySQL, you can use the LOAD DATA INFILE command for this.

Answer 3

Have a look at the HSSF serializer from the cocoon project.

The HSSF serializer catches SAX events and creates a spreadsheet in the XLS format used by Microsoft Excel