Merge PDF files with iText

The previous post described the use of iText to create a simple PDF. This post describes the use of iText to merge multiple PDF documents. The sample code here contains a method that will take the a list of PDF files as input, along with an OutputStream to which the merged PDF file will be written. This example also implements paging, i.e. along with merging the PDF files the merged PDF file also adds page numbers to the generated PDF file. The following is a brief description of the steps involved in merging PDF files using iText.
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1. Create a PdfReader for each input PDF file

   PdfReader pdfReader = new PdfReader(pdf);

2. Create a document object to represent the PDF.

   Document document = new Document();

3. Create a PdfWriter for the target OutputStream

   PdfWriter writer = PdfWriter.getInstance(document, outputStream);

4. Select a font with which the page numbers will be written

   BaseFont bf = BaseFont.createFont(BaseFont.HELVETICA, BaseFont.CP1252, BaseFont.NOT_EMBEDDED);

5. Create a a PdfContentByte object to hold the data of the merged PDF

   PdfContentByte cb = writer.getDirectContent();

6. Add individual pages from the source to the target.

   document.newPage();
   pageOfCurrentReaderPDF++;
   currentPageNumber++;
   page1 = writer.getImportedPage(pdfReader, pageOfCurrentReaderPDF);
   cb.addTemplate(page1, 0, 0);

7. Add page text at the bottom of the page

   cb.beginText();
   cb.setFontAndSize(bf, 9);
   cb.showTextAligned(PdfContentByte.ALIGN_CENTER, "Page " + currentPageNumber + " of " + totalPages, 520, 5, 0);
   cb.endText();

The following is the complete source code merging PDF files.

public class MergePDF {
  public static void main(String[] args) {
    try {
      List<InputStream> pdfs = new ArrayList<InputStream>();
      pdfs.add(new FileInputStream("c:\\pdf\\2.pdf"));
      pdfs.add(new FileInputStream("c:\\pdf\\3.pdf"));
      OutputStream output = new FileOutputStream("c:\\pdf\\merge.pdf");
      MergePDF.concatPDFs(pdfs, output, true);
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  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();
      }
    }
  }
}

MergePDF.java