What's the easiest way to merge (server-side) a collection of PDF documents into one big PDF document in JAVA

Question

I have 3 PDF documents that are generated on the fly by a legacy library that we use, and written to disk. What's the easiest way for my JAVA server code to grab these 3 documents and turn them into one long PDF document where it's just all the pages from document #1, followed by all the pages from document #2, etc.

Ideally I would like this to happen in memory so I can return it as a stream to the client, but writing it to disk is also an option.

Answer 1

@J D OConal, thanks for the tip, the article you sent me was very outdated, but it did point me towards iText.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();
            }
        }
    }
}

Answer 2

I've used pdftk to great effect. It's an external application that you'll have to run from your java app.