Christian Wahl

One of my interests is XML and with that interest, a tail of related technologies. Over the years I have spend a lot of time on XSL transforming “stuff”. From time to time I have also used Apache FOP, a tool for generating PDF files from XML using XSL formatting objects (XSL-FO). This tool require Java – like everything else – back then. But now, not so much. So, actually I don’t have Java installed.

The question is: how can I run FOP without all the hassle of installing Java? Here Docker comes to the rescue. From previous experiences with FOP I knew that I needed Sun/Oracle Java. I don’t know the details, but fortunately FOP version 2.5 can also run under OpenJDK. This made it even easier to get up and running.

Before getting into the details – this is the final Dockerfile:

FROM ubuntu

ENV PATH "$PATH:/usr/local/fop-2.5/fop"

RUN apt-get update
RUN apt-get install -y default-jre
RUN apt-get install -y wget

RUN wget http://ftp.download-by.net/apache/xmlgraphics/fop/binaries/fop-2.5-bin.tar.gz

RUN tar -xvzf fop-2.5-bin.tar.gz -C /usr/local

ENTRYPOINT ["fop"]
CMD ["-version"]

Details:

1. The starting point is the latest Ubuntu image: FROM ubuntu. I haven’t looked into other options.
2. To be able to call fop from the shell I need to add the path of the installation to the PATH environment variable: ENV PATH "$PATH:/usr/local/fop-2.5/fop". I struggled a lot with this, adding the path to /etc/profile and ~/.bashrc, and running both source /etc/profile and . /etc/profile etc. and finally ended with this simple solution.
3. I need both Java and wget installed. RUN apt-get update will download all the PPAs. And the running RUN apt-get install -y default-jre and RUN apt-get install -y wget, both with the -y flag will install the two applications. default-jre is an alias for OpenJDK.
4. Now, I can download the files for fop: RUN wget http://ftp.download-by.net/apache/xmlgraphics/fop/binaries/fop-2.5-bin.tar.gz.
5. And extract the tar.gz file into the /usr/local directory: RUN tar -xvzf fop-2.5-bin.tar.gz -C /usr/local.
6. Finally I add fop as the entrypoint: ENTRYPOINT ["fop"] and a default parameter: CMD ["-version"] to fop.

With the Docker file in place an image can be build:

$ docker build -t fop .

The container based on the image will just run as long as the process is running:

$ docker run -it --rm fop

Using Apache FOP

Just to give a practical (and short) example. This is the contents of helloworld.fo:

<?xml version="1.0" encoding="UTF-8"?>
<root xmlns="http://www.w3.org/1999/XSL/Format">
  <layout-master-set>
    <simple-page-master
      margin="10mm" page-width="210mm" page-height="297mm"
      master-name="simple">
      <region-body region-name="simple-body"
        margin-bottom="20mm" margin-top="20mm" />
    </simple-page-master>
  </layout-master-set>
  <page-sequence master-reference="simple">
    <flow flow-name="simple-body">
      <block>Hello World!</block>
    </flow>
  </page-sequence>
</root>

To generate a PDF file execute:

$ docker run --user $(id -u):$(id -g) -v $(pwd):/src -w /src -it --rm fop helloworld.fo helloworld.pdf

Where --user set the user to be you (instead of root), -v is mapping the current directory to /src, -w is setting the working directory to /src and fop helloworld.fo helloworld.pdf will generate a PDF file and save it in the working directory.