Stamping PDF files

In a previous post, I examined how we can use LiveCode and the Java-based iText library to concatenate a series of existing PDF files into a single PDF file. Now we will examine how we can 'stamp' a PDF file with an image using the same technique.

The first thing to code is the Java class that we will call using the shell function. Here's what I came up with:

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import com.lowagie.text.DocumentException;
import com.lowagie.text.Image;
import com.lowagie.text.Rectangle;
import com.lowagie.text.pdf.PdfContentByte;
import com.lowagie.text.pdf.PdfReader;
import com.lowagie.text.pdf.PdfStamper;

public class StampPdfFile {
  public static void main(String[] args) throws IOException, DocumentException {
    final String inputFile = args[0];
    final String outputFile = args[1];
    final String imageFile = args[2];
    final String[] coords = args[3].split(",");
    final PdfReader inputReader = new PdfReader(inputFile);
    final OutputStream outputStream = new FileOutputStream(outputFile);
    final PdfStamper outputStamper = new PdfStamper(inputReader, outputStream);
    final int pageCount = inputReader.getNumberOfPages();
    final Image image = Image.getInstance(imageFile);
    final int left = Integer.parseInt(coords[0]);
    final int top = Integer.parseInt(coords[1]);
    final int right = Integer.parseInt(coords[2]);
    final int bottom = Integer.parseInt(coords[3]);
    final int height = bottom - top;
    final int width = right - left;
    image.scaleToFit(width, height);
    for (int pageIndex = 1; pageIndex <= pageCount; pageIndex++) {
      final PdfContentByte overContent = outputStamper.getOverContent(pageIndex);
      final Rectangle pageSize = inputReader.getPageSize(pageIndex);
      image.setAbsolutePosition(left, pageSize.getHeight() - bottom);
      overContent.addImage(image);
    }
    outputStamper.close();
  }
}

In a nutshell, the first parameter is the input file, the second the output file, the third the image file, and the fourth parameter is a comma-separated list of coordinates making up the target rectangle. As usual, the code is a tad lazy when it comes to faulty input parameters and exception handling - if there's a mistake you'll simply get the stacktrace as the output of the shell command.

The most important bit is in the loop over the pages, where we use the outputStamper.getOverContent() method to draw our image on top of the existing content. If you'd rather have the image in the back, as a watermark, you would use the outputStamper.getUnderContent() methopd instead. Also note that setting the image position coordinate system works from the bottomLeft of the page, so we have to use the original page height and subtract the bottom coordinate from it.

Now we can proceed with writing a LiveCode button script:

on mouseUp
   --> determine the input, output and image files
   local tInputFile, tOutputFile, tImageFile
   put ShellPath(AbsolutePathFromStack("demo1.pdf")) \
          into tInputFile
   put ShellPath(AbsolutePathFromStack("stamp.pdf")) \
          into tOutputFile
   put ShellPath(AbsolutePathFromStack("Template.png")) \
          into tImageFile
   --> determine the image target rectangle
   local tImageRect
   put quote & "10,10,103,87" & quote \
          into tImageRect
   --> determine the class path
   local tClassPath
   if the platform is "Win32" then
      put ".;iText-2.1.7.jar" into tClassPath
   else
      put ".:iText-2.1.7.jar" into tClassPath
   end if
   --> assemble the shell command
   local tShellCommand
   put "java -classpath" && tClassPath && \
          "StampPdfFile" && \
          tInputFile && \
          tOutputFile && \
          tImageFile && \
          tImageRect \
          into tShellCommand
   --> execute the shell command
   local tHideConsoleWindows, tDefaultFolder, tShellResult
   put the hideConsoleWindows into tHideConsoleWindows
   set the hideConsoleWindows to true
   put the defaultFolder into tDefaultFolder
   set the defaultFolder to AbsolutePathFromStack()
   put shell(tShellCommand) into tShellResult
   set the defaultFolder to tDefaultFolder
   set the hideConsoleWindows to tHideConsoleWindows
   if tShellResult is not empty then
      answer error tShellResult
   end if
end mouseUp

function AbsolutePathFromStack pFileName
   local tAbsolutePath
   put the effective filename of this stack into tAbsolutePath
   set the itemDelimiter to slash
   if pFileName is not empty then
      put pFileName into item -1 of tAbsolutePath
   else
      delete item -1 of tAbsolutePath
   end if
   return tAbsolutePath
end AbsolutePathFromStack

function ShellPath pPath
   if the platform is "Win32" then
      put quote & pPath & quote into pPath
   else
      replace space with backslash & space in pPath
   end if
   return pPath
end ShellPath

Click the button, and it happily takes the existing PDF files (demo1.pdf), paints the image (Template.png) on top of all pages, and writes a new PDF file (stamp.pdf) in the same folder as our stack. There we have it, another example of using iText from within LiveCode.