iText tutorial:Merge PDF files using iText JAR

Previous article Generating PDF files using iText JAR had described a nice and basic way of generating PDF files in Java using iTest JAR. It is a great starter tutorial for those who wants to start working with iText.
In one of the requirement, I had to merge two or more PDF files and generate a single PDF file out of it. I thought of implementing the functionality from scratch in iText, but then thought to google it and see if already someone have written code for what I was looking for. As expected, I got a nice implementation of java code that merges 2 or more PDF files using iText jar. I thought of dissecting the code in this post and give credit to original author of the post.

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(); 

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();
      }
    }
  }
}

Thanks.