pdfBox add different lines to pdf

Question

I'm looking into generating a pdf-document. At the moment I'm trying out different approaches. I want to get more than one line in a pdf-document. Using a HelloWorld code example I came up with ...

package org.apache.pdfbox.examples.pdmodel;

import java.io.IOException;

import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;

import org.apache.pdfbox.pdmodel.PDPageContentStream;

import org.apache.pdfbox.pdmodel.font.PDFont;
import org.apache.pdfbox.pdmodel.font.PDType1Font;

/**
 * Creates a "Hello World" PDF using the built-in Helvetica font.
 *
 * The example is taken from the PDF file format specification.
 */
public final class HelloWorld
{
    private HelloWorld()
    {
    }

    public static void main(String[] args) throws IOException
    {

        String filename = "line.pdf";
        String message = "line";

        PDDocument doc = new PDDocument();
        try
        {
            PDPage page = new PDPage();
            doc.addPage(page);

            PDFont font = PDType1Font.HELVETICA_BOLD;

            PDPageContentStream contents = new PDPageContentStream(doc, page);
            contents.beginText();
            contents.setFont(font, 12);
            // Loop to create 25 lines of text
            for (int y = 0; y< 25; y++) {
                int ty = 700 + y * 15;
                contents.newLineAtOffset(100, ty);
                //contents.newLineAtOffset(125, ty);
                //contents.showText(Integer.toString(i));
                contents.showText(message + " " + Integer.toString(i));
                System.out.println(message + " " + Integer.toString(i));
            }
            contents.endText();
            contents.close();

            doc.save(filename);
        }
        finally
        {
            doc.close();
            System.out.println("HelloWorld finished after 'doc.close()'.");
        }
    }
}

But looking at my resulting document I only see "line 0" once, and no other lines. What am I doing wrong?

Answer 1

Your issue is that you think PDPageContentStream.newLineAtOffset uses absolute coordinates. This is not the case, it uses relative coordinates, cf. the JavaDocs:

/**
 * The Td operator.
 * Move to the start of the next line, offset from the start of the current line by (tx, ty).
 *
 * @param tx The x translation.
 * @param ty The y translation.
 * @throws IOException If there is an error writing to the stream.
 * @throws IllegalStateException If the method was not allowed to be called at this time.
 */
public void newLineAtOffset(float tx, float ty) throws IOException

So your additional lines are way off the visible page area.

Thus, you might want to something like this:

...
contents.beginText();
contents.setFont(font, 12);
contents.newLineAtOffset(100, 700);
// Loop to create 25 lines of text
for (int i = 0; i < 25; i++) {
    contents.showText(message + " " + Integer.toString(i));
    System.out.println(message + " " + Integer.toString(i));
    contents.newLineAtOffset(0, -15);
}
contents.endText();
...

Here you start at 100, 700 and move down for each line by 15.

Answer 2

In addition to mkl's answer you could also create a new text operation for each line. Doing that will enable you to use absolute coordinates.

...
contents.setFont(font, 12);
// Loop to create 25 lines of text
for (int i = 0; i < 25; i++) {
    int ty = 700 + y * 15;
    contents.beginText();
    contents.newLineAtOffset(100, ty);
    contents.showText(message + " " + Integer.toString(i));
    System.out.println(message + " " + Integer.toString(i))
    contents.endText();
}
...

Whether you need this or not depends on your usecase.
For example I wanted to write some text right aligned. In that case it was easier to use absolute position, so I created a helper method like this:

public static void showTextRightAligned(PDPageContentStream contentStream, PDType1Font font, int fontsize, float rightX, float topY, String text) throws IOException
{
    float textWidth = fontsize * font.getStringWidth(text) / 1000;
    float leftX = rightX - textWidth;
    contentStream.beginText();
    contentStream.newLineAtOffset(leftX, topY);
    contentStream.showText(text);
    contentStream.endText();
}