Generating PDF from XML in Java using ApacheFOP

Question

I am trying to generate on-the-fly PDF reports from Java objects. I have not been able to find many examples of this, so I have been following this example:

http://svn.apache.org/viewvc/xmlgraphics/fop/trunk/examples/embedding/java/embedding/ExampleObj2PDF.java?view=markup

The only real difference between this code and my own is that I generate src (line 81 in the example) using JSON conversion and an XMLSerializer.

The problem I run into is using the Transformer. When I do the transform (line 87 of the example), I receive the error message:

(Location of error unknown)org.apache.fop.fo.ValidationException: First element must be the fo:root formatting object. Found (Namespace URI: "", Local Name: "html") instead. Please make sure you're producing a valid XSL-FO document.

Since I don't have visibility into the Transformer, and haven't been able to find the kind of documentation to tell me how it is supposed to work, I don't really know where the transformation is breaking down.

Any experience with this kind of conversion, or understand of whatever it is I'm missing is greatly appreciated.

Answer 1

The input of Apache FOP is XSL:FO. The error message is saying that the input is not a valid XSL:FO document because the first (root) element is expected to be "fo:root" but "html" was found. FOP does not read HTML input. I suggest to break down the code in smaller steps and save the intermediate documents to help you identify the problem. The steps are:

1. JSON object is serialized to XML
2. XML is transformed using an XSLT to XSL:FO
3. XSL:FO is transformed using FOP to PDF.