@J D OConal, thanks for the tip, the article you sent me was very outdated, but it did point me towards iText. I found this page that explains how to do exactly what I need:
http://java-x.blogspot.com/2006/11/merge-pdf-files-with-itext.html
Thanks for the other answers, but I don't really want to have to spawn other processes if I can avoid it, and our project already has itext.jar, so I'm not adding any external dependancies
Here's the code I ended up writing:
public class PdfMergeHelper {
/**
* Merges the passed in PDFs, in the order that they are listed in the java.util.List.
* Writes the resulting PDF out to the OutputStream provided.
*
* Sample Usage:
* List<InputStream> pdfs = new ArrayList<InputStream>();
* pdfs.add(new FileInputStream("/location/of/pdf/OQS_FRSv1.5.pdf"));
* pdfs.add(new FileInputStream("/location/of/pdf/PPFP-Contract_Genericv0.5.pdf"));
* pdfs.add(new FileInputStream("/location/of/pdf/PPFP-Quotev0.6.pdf"));
* FileOutputStream output = new FileOutputStream("/location/to/write/to/merge.pdf");
* PdfMergeHelper.concatPDFs(pdfs, output, true);
*
* @param streamOfPDFFiles the list of files to merge, in the order that they should be merged
* @param outputStream the output stream to write the merged PDF to
* @param paginate true if you want page numbers to appear at the bottom of each page, false otherwise
*/
public static void concatPDFs(List<InputStream> streamOfPDFFiles, OutputStream outputStream, boolean paginate) {
Document document = new Document();
try {
List<InputStream> pdfs = streamOfPDFFiles;
List<PdfReader> readers = new ArrayList<PdfReader>();
int totalPages = 0;
Iterator<InputStream> iteratorPDFs = pdfs.iterator();
// Create Readers for the pdfs.
while (iteratorPDFs.hasNext()) {
InputStream pdf = iteratorPDFs.next();
PdfReader pdfReader = new PdfReader(pdf);
readers.add(pdfReader);
totalPages += pdfReader.getNumberOfPages();
}
// Create a writer for the outputstream
PdfWriter writer = PdfWriter.getInstance(document, outputStream);
document.open();
BaseFont bf = BaseFont.createFont(BaseFont.HELVETICA, BaseFont.CP1252, BaseFont.NOT_EMBEDDED);
PdfContentByte cb = writer.getDirectContent(); // Holds the PDF
// data
PdfImportedPage page;
int currentPageNumber = 0;
int pageOfCurrentReaderPDF = 0;
Iterator<PdfReader> iteratorPDFReader = readers.iterator();
// Loop through the PDF files and add to the output.
while (iteratorPDFReader.hasNext()) {
PdfReader pdfReader = iteratorPDFReader.next();
// Create a new page in the target for each source page.
while (pageOfCurrentReaderPDF < pdfReader.getNumberOfPages()) {
document.newPage();
pageOfCurrentReaderPDF++;
currentPageNumber++;
page = writer.getImportedPage(pdfReader, pageOfCurrentReaderPDF);
cb.addTemplate(page, 0, 0);
// Code for pagination.
if (paginate) {
cb.beginText();
cb.setFontAndSize(bf, 9);
cb.showTextAligned(PdfContentByte.ALIGN_CENTER, "" + currentPageNumber + " of " + totalPages,
520, 5, 0);
cb.endText();
}
}
pageOfCurrentReaderPDF = 0;
}
outputStream.flush();
document.close();
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (document.isOpen()) {
document.close();
}
try {
if (outputStream != null) {
outputStream.close();
}
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}
}