NPE with StaxEventWriter's Result object

[flurdy]

Hi we are getting an unexplained NullPointerException in StaxEventItemWriter.


Our Xml looks something like this:

<bean id="blahWriter" class="org.springframework.batch.item.xml.StaxEventItemWriter"  scope="step">
 		<property name="resource" value="file:///C:/blah/blah/blah.tmp"/>
 		<property name="rootTagName" value="root" />
		<property name="overwriteOutput" value="true" />
		<property name="marshaller" ref="filesMarshaller" />
 	</bean>
 	 	
	<bean id="filesMarshaller" class="org.springframework.oxm.xstream.XStreamMarshaller">
	....

And in our step the writer fails with this:

java.lang.NullPointerException
    at org.springframework.oxm.support.AbstractMarshaller.marshal(AbstractMarshaller.java:105)
    at org.springframework.batch.item.xml.StaxEventItemWriter.write(StaxEventItemWriter.java:574)

Line 573 & 574 of StaxEventWriter

Result result = StaxUtils.getResult(eventWriter);
		marshaller.marshal(object, result );

Line 105 of AbstractMarshaller after failing some instanceof checks on result as it is probably null:

throw new IllegalArgumentException("Unknown Result type: " + result.getClass())

And this line then throws an NPE as you cant access .getClass() on a null object.


At first wasted alot of time wondering if StaxUtils.getResult method could not detect Spring environment (line 116-126 of StaxUtils), but it now more seems the invoke call fails to create a Result object. I think. Line 117 of StaxUtils:

if (hasSpring30StaxSupport) {
			Object result = staxUtilsResultMethodOnSpring30.invoke(null,w);
			Assert.isInstanceOf(Result.class, result, "the result should be assignable to " + Result.class.getName());
			return (Result) result;

staxUtilsResultMethodOnSpring30 seems to be invoke a createStaxResult method on XMLEventWriter? (Line 78 of StaxUtils). This is where my reflection knowledge suffers.

staxUtilsResultMethodOnSpring30 = ClassUtils.getStaticMethod(clzz, "createStaxResult", new Class[]{XMLEventWriter.class});

Any ideas of what can cause our stax step not to create a proper Result object?

[flurdy]

As StaxEventItemWriter can not be used as it always throws NullPointerException we are currently rewriting this to a custom item writer to marshal to xml and append to a file.

Shame, as StaxEventItemWriter seemed such a clean way of doing it