Determine PNG image start/end in a Fop stream.

[Eugene Smola]

Hello,

I use Apache FOP to generate PDFs and PNGs from given xml content (content.xml) and xsl markup (markup.xsl).
If there is a long content.xml file it perfectly generates e.g. 3-page PDF and 3 different PNG files.
There is no problems if I store it on filesystem.

But if I want the PNG to be printed out directly in a Servlet output stream it gives only the first file.

protected void doGet(HttpServletRequest request, HttpServletResponse response) {
response.setContentType(mime);
String mime = "image/png";
ByteArrayOutputStream imageStream = getImageStream(mime);
OutputStream responseOutStream = response.getOutputStream();
imageStream.writeTo(responseOutStream);
...
}

The getImageStream method is only makes transformation and returns the output stream which contains 3 PNG files:

public ByteArrayOutputStream getImageStream (String mime) throws Exception {
		StreamSource contentSource = new StreamSource(xmlContentStream);

		StreamSource transformSource = new StreamSource(xslMarkupStream);
		
		FopFactory fopFactory = FopFactory.newInstance();
		FOUserAgent foUserAgent = fopFactory.newFOUserAgent();
		
		ByteArrayOutputStream outStream = new ByteArrayOutputStream();

		Transformer xslfoTransformer = getTransformer(transformSource);

		Fop fop = fopFactory.newFop(mime, foUserAgent, outStream);
		
		// Resulting SAX events (the generated FO)
		// must be piped through to FOP
		Result res = new SAXResult(fop.getDefaultHandler());

		// Start XSLT transformation and FOP processing

		// everything will happen here..
		xslfoTransformer.transform(contentSource, res);
		xmlContentStream.close();
		xslMarkupStream.close();
		return outStream;
	}

Is there any way to force it to give all three PNG files?

I don't want to store temporary files on server, is there any way to do it just writing the Fop outputstream content into Servlet response output stream?

Thank you.

[Paul Clapham]

I don't quite understand your description of the data. But I have to say that the idea of sending three concatenated PNG files as the response to an HTTP request is a bad idea. Whatever sent the request is expecting a single file as the response. A single PDF file which contains three embedded images would be fine; a PNG image would also be fine. But three images lumped together is not fine.

[Eugene Smola]

Agree. That's why it is not working, I think.

But is that possible to determine in the Fop output stream where the first PNG stops and second starts and do e.g. download button for each? As what Fop gives is the only output stream where three PNGs hidden.

[g tsuji]

One possible way to do, asking for less trouble, is to form the output image in tiff (mime "image/tiff") all in one piece.

[Eugene Smola]

Thank you. That sounds like the most appropriate way of doing so.