Adding up ByteArrayOutputStreams

Question

Im having a bunch of ByteArrayOutputstreams onto which pdf reports are written over different parts of a particular workflow. I use IText to accomplish this. Now, at the end I would like to group all these single ByteArrayOutputstreams into a bigger ByteArrayOutputstream so as to group all pdf reports together.

I looked at Apache Commons library but could not find anything of use.

1 way that i know of is to convert each of these ByteArrayOutputstreams into byte[] and then using System.arraycopy to copy them into a bigger byte[]. The problem with this is me having to declare the size of the result byte[] upfront which makes it non-ideal.

Is there any other way to copy/append to/concatenate ByteArrayOutputStreams taht i may have missed ?

Answer 1

You can use a List<Byte[]> for that. You can add your bytes on the go to the list.

List<Byte[]> listOfAllBytes = new ArrayList<Byte[]>;
ByteArrayOutputstreams byteArray = //...
listOfAllBytes.add(byteArray.toByteArray);

At the end, you can just get the full byte array back.

Answer 2

Write all but one of their toByteArray() results into the remaining one.

Answer 3

public class Concatenate {

    /** The resulting PDF file. */
    public static final String RESULT
        = "path/to/concatenated_pdf.pdf";

    public static void main(String[] args)
        throws IOException, DocumentException {
        String[] files = { "1.pdf", "2.pdf" };
        Document document = new Document();
        PdfCopy copy = new PdfCopy(document, new FileOutputStream(RESULT));
        document.open();
        PdfReader reader;
        int n;
        // loop over the documents you want to concatenate
        for (int i = 0; i < files.length; i++) {
            reader = new PdfReader(files[i]);
            // loop over the pages in that document
            n = reader.getNumberOfPages();
            for (int page = 0; page < n; ) {
                copy.addPage(copy.getImportedPage(reader, ++page));
            }
            copy.freeReader(reader);
        }
        document.close();
    }
}