Apache FOP in a Java Applet - No ImagePreloader found for data

Question

I\'m looking at an issue in a mature commercial product.

In a nutshell, we are using part of the Apache POI library to read in a Word .DOC or .DOCX file, and convert

Answer 1

Just been struggling with this one. If you're using the maven-shade-plugin to create an uber jar, use the ServicesResourceTransformer to merge all the services configuration:

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-shade-plugin</artifactId>
  <version>2.2</version>
  <executions>
    <execution>
      <!-- snip -->
      <configuration>
        <transformers>
          <!-- snip -->
          <transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
        </transformers>
      </configuration>
    </execution>
  </executions>
</plugin>

Answer 2

In my case the plugin registry loaded ImagePreloaders from both the plugin files and mixed them together. Yet the error still appeared. I was inserting an SVG file into a PDF file. The root cause was incorrect version of org.apache.xmlgraphics:batik-svg-dom. The 1.7 version was required by the org.apache.xmlgraphics:fop:1.1, however, the 1.8 version was on the classpath.

There is a key difference between the two versions: the org.apache.fop.image.loader.batik.PreloaderSVG class needs org.apache.batik.dom.svg.SAXSVGDocumentFactory from the version 1.7 on the classpath. If it gets org.apache.batik.anim.dom.SAXSVGDocumentFactory from the 1.8 version it does not work as expected.

This SO question: Where has org.apache.batik.dom.svg.SVGDOMImplementation gone? was helpful to me when resolving this issue.

Answer 3

In case anyone else has something similar, this turned out to be caused by the way the project was being built in Maven.

Fop 1.0 and above use the xml-graphics-commons library to facilitate the image rendering. As mentioned in the question, this uses a plugin registry which is configured using the following files inside the JAR:

META-INF/services/org.apache.xmlgraphics.image.loader.spi.ImageConverter
META-INF/services/org.apache.xmlgraphics.image.loader.spi.ImageLoaderFactory
META-INF/services/org.apache.xmlgraphics.image.loader.spi.ImagePreloader

...each of these contains a list of the image decoders which will be supported.

The problem is that xml-graphics-common ships these files with a sensible list of defaults, while FOP also has a conflicting set of defaults, which for some weird reason disable all of the image decoders, and that one was taking priority.

To solve the problem, I made sure that my maven pom.xml file imported xml-graphics-common before FOP, so that its defaults took precedence, and at that point everything sprang to life.

I am still not sure why the code was working correctly as a standalone test program, but I suspect it was the way the classpath was being handled being different to it running in plugin mode.