Question

Search as I may I have not found a solution to my problem here and I’m hoping the combined minds of StackOverflow will push me in the right direction.

My problem is as follows, I’m developing a print and print preview portion of a messaging system’s user agent. I was given specific XSLT templates that after transforming XML will produce a Formatting Objects document. With Apache FOP I’ve been able to render the FO document into PDF which is all fine and good, but I would also like to display it in a print preview dialog. Apache FOP contains such a class called PreviewDialog which requires in its constructor a FOUserAgent, which I can generate, and an object implementing the Renderable Interface.

The Renderable Interface has one implementing class in the FOP package which is called InputHandler which takes in its constructor a standard io File object. Now here is where the trouble begins. I’m currently storing the FO document as a temp file and pass this as a File object to an InputHandler instance which is then passed to the PreviewDialog. I see the dialog appear on my screen and along the bottom in a status bar it says that it is generating the document, and that is all it does.

Here is the code I’m trying to use. It isn’t production code so it’s not pretty:

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Random;

import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.sax.SAXResult;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

import org.apache.fop.apps.FOPException;
import org.apache.fop.apps.FOUserAgent;
import org.apache.fop.apps.Fop;
import org.apache.fop.apps.FopFactory;
import org.apache.fop.cli.InputHandler;
import org.apache.fop.render.awt.viewer.PreviewDialog;

public class PrintPreview {

    public void showPreview(final File xslt, final File xmlSource) {
        boolean err = false;
        OutputStream out = null;
        Transformer transformer = null;

        final String tempFileName = this.getTempDir()
                + this.generateTempFileName();
        final String tempFoFile = tempFileName + ".fo";
        final String tempPdfFile = tempFileName + ".pdf";
        System.out.println(tempFileName);

        final TransformerFactory transformFactory = TransformerFactory
                .newInstance();
        final FopFactory fopFactory = FopFactory.newInstance();

        try {
            transformer = transformFactory
                    .newTransformer(new StreamSource(xslt));
            final Source src = new StreamSource(xmlSource);
            out = new FileOutputStream(tempFoFile);
            final Result res = new StreamResult(out);

            transformer.transform(src, res);
            System.out.println("XSLT Transform Completed");
        } catch (final TransformerConfigurationException e) {
            err = true;
            e.printStackTrace();
        } catch (final FileNotFoundException e) {
            err = true;
            e.printStackTrace();
        } catch (final TransformerException e) {
            err = true;
            e.printStackTrace();
        } finally {
            if (out != null) {
                try {
                    out.close();
                } catch (final IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

        System.out.println("Initializing Preview");
        transformer = null;
        out = null;
        final File fo = new File(tempFoFile);
        final File pdf = new File(tempPdfFile);

        if (!err) {

            final FOUserAgent ua = fopFactory.newFOUserAgent();
            try {
                transformer = transformFactory.newTransformer();
                out = new FileOutputStream(pdf);
                out = new BufferedOutputStream(out);

                final Fop fop = fopFactory.newFop(
                        MimeConstants.MIME_PDF, ua,
                            out);

                final Source foSrc = new StreamSource(fo);
                final Result foRes = new SAXResult(fop.getDefaultHandler());

                transformer.transform(foSrc, foRes);

                System.out.println("Transformation Complete");

        } catch (final FOPException e) {
            err = true;
            e.printStackTrace();
        } catch (final FileNotFoundException e) {
            err = true;
            e.printStackTrace();
        } catch (final TransformerException e) {
            err = true;
            e.printStackTrace();
        } finally {
            if (out != null) {
                try {
                    out.close();
                } catch (final IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

        if (!err) {
            System.out.println("Attempting to Preview");
            final InputHandler inputHandler = new InputHandler(fo);

            PreviewDialog.createPreviewDialog(ua, inputHandler, true);
        }
    }

    // perform the clean up
    // f.delete();

}

private String getTempDir() {

    final String p = "java.io.tmpdir";

    return System.getProperty(p);

}

private String generateTempFileName() {
    final String charset = "abcdefghijklmnopqrstuvwxyz1234567890abcdefghijklmnopqrstuvwxyz1234567890";
    final StringBuffer sb = new StringBuffer();
    Random r = new Random();
    int seed = r.nextInt();
    r = new Random(seed);
    for (int i = 0; i < 8; i++) {
        final int n = r.nextInt(71);
        seed = r.nextInt();
        sb.append(charset.charAt(n));
        r = new Random(seed);
    }

    return sb.toString();
}

}

Any help on this would be appreciated.

Answer 1

The answer it seems to give up on trying to use the preview dialog in Apache FOP, and instead use Apache PDFBox to generate the print preview using the PDFPagePanel class to display the changes.