Batik SVGGraphics2D nullpointerexception when drawing image

Question

I'm trying to use the Batik library to draw a BufferedImage to a SVG file. I have very similar code working fine for EPS/PS files, but for some reason the following code:

// Get a DOMImplementation and create an XML document
DOMImplementation domImpl = GenericDOMImplementation.getDOMImplementation();
Document document = domImpl.createDocument(null, "svg", null);

// Create an instance of the SVG Generator
SVGGraphics2D svgGenerator = new SVGGraphics2D(document);

// draw from image into the svg:
svgGenerator.drawImage(image,new RescaleOp((float)1.0,(float)0.0,null),0,0); 

// Write svg file
OutputStream outputStream = new FileOutputStream(svgFile);
Writer out = new OutputStreamWriter(outputStream, "UTF-8");

//svgGenerator.stream(out, true /* use css */);  

// write and close file:                   
outputStream.flush();
outputStream.close();

Results in a NullPointerException on the svgGenerator.drawImage(...) line. Since basically the same command is working for a AbstractPSDocumentGraphics2D (in another method) I have no idea what's wrong here.

Edit: image is declared elsewhere (a class variable, this code is inside a method of that class).

Here is a stacktrace:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at org.apache.batik.svggen.ImageHandlerBase64Encoder.encodeImage(ImageHandlerBase64Encoder.java:157)
at org.apache.batik.svggen.ImageHandlerBase64Encoder.handleHREF(ImageHandlerBase64Encoder.java:133)
at org.apache.batik.svggen.ImageHandlerBase64Encoder.handleHREF(ImageHandlerBase64Encoder.java:72)
at org.apache.batik.svggen.DefaultImageHandler.handleImage(DefaultImageHandler.java:63)
at org.apache.batik.svggen.SimpleImageHandler.handleImage(SimpleImageHandler.java:100)
at org.apache.batik.svggen.SVGGraphics2D.drawImage(SVGGraphics2D.java:677)
at org.apache.batik.svggen.SVGGraphics2D.drawImage(SVGGraphics2D.java:996)
at SciTK.SciTK_Image.exportImageAsSVG(SciTK_Image.java:1232)
at SciTK.SciTK_Image.save_image(SciTK_Image.java:428)
at SciTK.SciTK_Image$7.actionPerformed(SciTK_Image.java:982)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.AbstractButton.doClick(AbstractButton.java:376)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:833)
at com.apple.laf.AquaMenuItemUI.doClick(AquaMenuItemUI.java:157)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:877)
at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:289)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

Answer 1

For the sake of others googling this... I had - I believe - the same issue.

Assuming Batik 1.7: The low-level cause is: ImageHandlerBase64Encoder.encodeImage() calls:

ImageWriter writer = ImageWriterRegistry.getInstance().getWriterFor("image/png");
writer.writeImage(buf, os);

and the ImageWriterRegistry is empty, so it returns null from getWriterFor("image/png") hence writer.writeImage(buf, os); dies.

The cause of the registry being empty is missing JAR(s) in the Classpath. I think what is specifically required is batik-codec.jar, but I just added all the batik JARs.

You can download batik sources and see in debugger that with the JARs the "image/png" and other formats get registered (the first call to ImageWriterRegistry.getInstance() creates the instance, its constructor calls setup() which in turn iterates over all ImageWriter service providers - which should be a non-empty set with the correct Classpath.)