Return Excel downloadable file from Spring

Question

So I have a Spring controller, and I'd like to create an Excel file and return it so that it is downloaded by the browser.

I'm using JEXcelApi.

This is my controller code

@RequestMapping(value="/excel/cols/{colString}/rows/{rowString}/", method = RequestMethod.GET)
@ResponseBody
public ResponseEntity<String> exportExcel(HttpServletResponse response,
    @PathVariable List<String> colString,
    @PathVariable List<String> rowString) throws JSONException, IOException, WriteException {
    WritableWorkbook workbook = Workbook.createWorkbook(new File("exported.xls"));
    WritableSheet sheet = workbook.createSheet("Exported",0);
    String[] cols = colString.get(0).split(",");
    String[] rows = rowString.get(0).split(","); 
    for(int i = 0; i < cols.length;i++){
        Label label = new Label(i,0, cols[i]);
        sheet.addCell(label);
    }
    int excelCol = 0;
    int excelRow = 1;
    for(int i = 0; i < rows.length;i++){
        Label label = new Label(excelCol,excelRow, rows[i]);
        sheet.addCell(label);
        excelCol++;
        if((i+1) % cols.length == 0){
            excelCol = 0;
            excelRow++;
        }
    }
    workbook.write();
    workbook.close();
    return null;
}

How do I do that? I suspect there's some content header I can set. I know one method is to use Spring's Abstract Excel view class, but is there a simpler method?

Solution

You need to set the Content-Disposition header.

response.setHeader("Content-disposition","attachment; filename=" + yourFileName);

and write your bytes directly to the response OutputStream.

File xls = new File("exported.xls"); // or whatever your file is
FileInputStream in = new FileInputStream(xls);
OutputStream out = response.getOutputStream();

byte[] buffer= new byte[8192]; // use bigger if you want
int length = 0;

while ((length = in.read(buffer)) > 0){
     out.write(buffer, 0, length);
}
in.close();
out.close();

---

The above is relatively old. You can construct a ResponseEntity with FileSystemResource now. A ResourceHttpMessageConverter will then copy the bytes, as I have suggested above, for you. Spring MVC makes it simpler for you rather than having you interact with interfaces from the Servlet specification.

Comments

[praks5432]

ah so what then gets returned?

[praks5432]

ah, is there any chance you could write the writing to stream code?

[praks5432]

so I tried that - but nothing is downloading, instead what's happening is something is console logging out - this is coming from the success function from my client

[praks5432]

oh one more question - is there a way to dynamically alter the buffer array - because if the file is very big, this method won't work right?