org.apache.fop.fo.flow.ExternalGraphic catches and logs ImageException I want to handle myself

Question

I am transforming an Image into pdf for test purposes.

To ensure that the Image is compatible with the printing process later on, I'm running a quick test print during the upload.

I'm creating a simple Test-PDF with a transformer. When I try to print an image with an incompatible format, the ImageManager of the transformer throws an ImageException, starting in the preloadImage() function:

  public ImageInfo preloadImage(String uri, Source src)
            throws ImageException, IOException {
        Iterator iter = registry.getPreloaderIterator();
        while (iter.hasNext()) {
            ImagePreloader preloader = (ImagePreloader)iter.next();
            ImageInfo info = preloader.preloadImage(uri, src, imageContext);
            if (info != null) {
                return info;
            }
        }
        throw new ImageException("The file format is not supported. No ImagePreloader found for "
                + uri);
    }

throwing it to:

   public ImageInfo needImageInfo(String uri, ImageSessionContext session, ImageManager manager)
                throws ImageException, IOException {
            //Fetch unique version of the URI and use it for synchronization so we have some sort of
            //"row-level" locking instead of "table-level" locking (to use a database analogy).
            //The fine locking strategy is necessary since preloading an image is a potentially long
            //operation.
            if (isInvalidURI(uri)) {
                throw new FileNotFoundException("Image not found: " + uri);
            }
            String lockURI = uri.intern();
            synchronized (lockURI) {
                ImageInfo info = getImageInfo(uri);
                if (info == null) {
                    try {
                        Source src = session.needSource(uri);
                        if (src == null) {
                            registerInvalidURI(uri);
                            throw new FileNotFoundException("Image not found: " + uri);
                        }
                        info = manager.preloadImage(uri, src);
                        session.returnSource(uri, src);
                    } catch (IOException ioe) {
                        registerInvalidURI(uri);
                        throw ioe;
                    } catch (ImageException e) {
                        registerInvalidURI(uri);
                        throw e;
                    }
                    putImageInfo(info);
                }
                return info;
            }
        }

throwing it to :

public ImageInfo getImageInfo(String uri, ImageSessionContext session)
                throws ImageException, IOException {
        if (getCache() != null) {
            return getCache().needImageInfo(uri, session, this);
        } else {
            return preloadImage(uri, session);
        }
    }

Finally it gets caught and logged in the ExternalGraphic.class:

 /** {@inheritDoc} */
    public void bind(PropertyList pList) throws FOPException {
        super.bind(pList);
        src = pList.get(PR_SRC).getString();

        //Additional processing: obtain the image's intrinsic size and baseline information
        url = URISpecification.getURL(src);
        FOUserAgent userAgent = getUserAgent();
        ImageManager manager = userAgent.getFactory().getImageManager();
        ImageInfo info = null;
        try {
            info = manager.getImageInfo(url, userAgent.getImageSessionContext());
        } catch (ImageException e) {
            ResourceEventProducer eventProducer = ResourceEventProducer.Provider.get(
                    getUserAgent().getEventBroadcaster());
            eventProducer.imageError(this, url, e, getLocator());
        } catch (FileNotFoundException fnfe) {
            ResourceEventProducer eventProducer = ResourceEventProducer.Provider.get(
                    getUserAgent().getEventBroadcaster());
            eventProducer.imageNotFound(this, url, fnfe, getLocator());
        } catch (IOException ioe) {
            ResourceEventProducer eventProducer = ResourceEventProducer.Provider.get(
                    getUserAgent().getEventBroadcaster());
            eventProducer.imageIOError(this, url, ioe, getLocator());
        }
        if (info != null) {
            this.intrinsicWidth = info.getSize().getWidthMpt();
            this.intrinsicHeight = info.getSize().getHeightMpt();
            int baseline = info.getSize().getBaselinePositionFromBottom();
            if (baseline != 0) {
                this.intrinsicAlignmentAdjust
                    = FixedLength.getInstance(-baseline);
            }
        }
    }

That way it isn't accessible for me in my code that uses the transformer.

I tried to use a custom ErrorListener, but the transformer only registers fatalErrors to the ErrorListener.

Is there any way to access the Exception and handle it myself without changing the code of the library?

Answer 1

It was easier than I thought. Before I call the transformation I register a costum EventListener to the User Agent of the Fop I'm using. This Listener just stores the Information what kind of Event was triggered, so I can throw an Exception if it's an ImageError.

My Listener:

import org.apache.fop.events.Event;
import org.apache.fop.events.EventListener;

public class ImageErrorListener implements EventListener
{

       private String eventKey = "";
private boolean imageError = false;

@Override
public void processEvent(Event event)
{
eventKey = event.getEventKey();
if(eventKey.equals("imageError")) {
    imageError = true;
}
}


public String getEventKey()
{
    return eventKey;
}


public void setEventKey(String eventKey)
{
    this.eventKey = eventKey;
}


public boolean isImageError()
{
    return imageError;
}


public void setImageError(boolean imageError)
{
    this.imageError = imageError;
}    
}

Use of the Listener:

// Start XSLT transformation and FOP processing
    ImageErrorListener imageListener = new ImageErrorListener();

    fop.getUserAgent().getEventBroadcaster().addEventListener(imageListener);
    if (res != null)
    {

        transformer.transform(xmlDomStreamSource, res);
    }

    if(imageListener.isImageError()) {
        throw new ImageException("");
    }

fop is of the type Fop ,xmlDomStreamSource ist the xml-Source I want to transform and res is my SAXResult.