Thanks a lot Josh. It solved the problem, but I still have a question about
your close method. Is the file mapped in memory so there is no IO?
Josh Micich wrote:
>
> This issue is not really specific to POI. The problem is that streams
> provide mostly sequential access to data. The code as you have
> written just writes two complete workbooks to the same stream (Excel
> probably silently ignores the second one).
>
> Theoretically, POI could have been written to provide non-stream based
> output (i.e. only 'dirty' parts of the workbook would be written out
> when requested), but this would be very complicated to implement. I
> would hazard a guess that even Excel uses plain stream based output.
>
> Below is some code that I hope is useful.
>
> ----
> // For clarity, the following code will work (but seems to be what you
> wanted to avoid):
> File file = new File("/tmp/Test.xls");
> OutputStream os;
>
> cell.setCellValue(1.5);
> os = new FileOutputStream(file);
> workbook.write(os);
> os.close();
>
> cell.setCellValue(3.5);
> os = new FileOutputStream(file); // re-open stream here
> workbook.write(os);
> os.close();
>
>
> ---------
> // Alternatively, if you are really keen on holding onto a single file
> handle, you could try something like this:
>
> File file = new File("/tmp/Test.xls");
> ResettableOutputSteam os = new ResettableOutputSteam(file);
>
> cell.setCellValue(1.5);
> os.reset();
> workbook.write(os);
> os.close();
>
> cell.setCellValue(3.5);
> os.reset();
> workbook.write(os);
> os.close();
>
> // ResettableOutputStream wraps a RandomAccessFile and extends
> OutputStream.
> // Here is a rough draft of something that should work
> public final class ResettableOutputStream extends OutputStream {
>
> private final RandomAccessFile _raf;
>
> public ResettableOutputStream(File f) throws FileNotFoundException {
> _raf = new RandomAccessFile(f, "rw");
> }
> public void write(int b) throws IOException {
> _raf.write(b);
> }
> public void write(byte[] b, int off, int len) throws IOException {
> _raf.write(b, off, len);
> }
> public void close() throws IOException {
> _raf.setLength(_raf.getFilePointer());
> }
> public void reset() throws IOException {
> _raf.seek(0);
> }
> }
>
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