How to generate PDFs from XML using Apache FOP in Ruby on Rails

The title is a bit of a mouthful. Sorry.

Before we begin, I present the caveat that this code should not be used on a production system. It launches a java runtime for every single request, which would cripple you. This would need (a) output caching, and (b) some sort of persistent FOP server process before it could be considered usable.

But if you just need to generate PDFs on an intranet app, say, then this could be handy.

Step 1: Put FOP somewhere it can be found. Specifically, its “build” and “lib” folders. I created a “fop” directory in my project, and stuck everything in there. (I don’t promise that this is ideologically sound — I’m new to the whole Rails thing.)

Step 2: Add Mime::Type.register "application/pdf", :pdf to config/initializers/mime_types.rb (this gleaned from Dynamic Graphics with Rails 1.2).

Step 3: Use a controller action something like this:

# GET /documents/1
# GET /documents/1.xml
# GET /documents/1.pdf
def show
  @document = Document.find(params[:id])

  respond_to do |format|
    format.html # show.html.erb
    format.xml { render :xml => @document }
    format.pdf do
      # We generate the classpath by scanning the FOP lib directory
      command = "java -cp #{Dir.getwd}/fop/build/fop.jar"
      Dir.foreach("fop/lib") do |file|
        command << ":#{Dir.getwd}/fop/lib/#{file}" if (file.match(/.jar/))
      end
      command << " org.apache.fop.cli.Main "
      command << " -xml #{Dir.getwd}/fop/xml/#{@document.file}"
      command << " -xsl #{Dir.getwd}/fop/xslt/doc2fo.xsl"
      command << " -pdf #{Dir.getwd}/fop/tmp/#{@document.id}.pdf"
      if(Kernel.system command) then
          send_file "#{Dir.getwd}/fop/tmp/#{@document.id}.pdf",
            :type => "application/pdf"
      else
          render :text => command
      end
    end
  end
end

Then whenever someone asks for “documents/17.pdf” it’ll make a PDF and serve it right on up. In the event that something goes wrong it’ll just display the command it ran, for some rough-and-ready debugging.

For a proof-of-concept you could try this with the example XML and XSLT that comes with FOP. Look for “projectteam2fo.xsl” in the examples directory.

As I said above, this works, but should not be put anywhere near a publicly accessible site.